An individual who is, or immediately before visiting a Contracting State was, a resident of the other Contracting State and is temporarily present in the first-mentioned Contracting State for the primary purpose of teaching, giving lectures or conducting research at a university, college, school or other accredited educational institution or scientific research institution in the first mentioned Contracting State shall be exempt from tax in the first mentioned Contracting State for a period not exceeding three years in the aggregate in respect of remuneration for such teaching, lectures or research.
既然是「aggregate」，所以无需是连续的 3 年，若中途离开美国、回到中国、之后再次回来美国，仍然可以接着计算。参见 IRS 在这份文件里举的例子：Thus, for example, a resident of China who visits the United States to conduct research at the National Institute of Health (NIH) for two years, 1986 and 1987, returns to China for a year, and then comes back for another year of research at NIH in 1989 would be exempt from tax on his NIH remuneration for each of the three years. However, if he stayed at NIH in 1990 or returned at a later time the exemption would no longer be available 。
It is the purpose of[the exemption under Article 18 of the 1945 U.K. treaty] that such exemption shall cease at the end of 2 years from the date of[the individual’s] initial arrival in the United States. Thus, if[the individual] reaches the United States on July 1, 1945, he is exempt with respect to his remuneration earned in the United States up to June 30, 1947.
Whether an individual who is present in the United States solely for the purpose of education, training, or obtaining special technical experience and who receives benefits under Article 20 (Students and Trainees) of the U.S.-China Income Tax Treaty (the “Treaty” or the “Chinese treaty”) may, without leaving the United States (or without leaving the United States for a period of more than one year), begin employment as a teacher, lecturer, or researcher in the United States and receive benefits under Article 19 (Teachers, Professors and Researchers) of the Treaty.
Yes, the individual may receive benefits under Article 19 of the Treaty provided
the individual is a resident of China for the year at issue or was a resident of China immediately before visiting the United States as a student or trainee;
the individual is “temporarily present” (notwithstanding the fact that the individual was present in the United States in prior years solely for educational or training purposes) in the United States for the year at issue for the primary purpose of teaching, giving lectures, or conducting research;
the individual’s teaching, lecturing, or research activities take place at a university, college, school, or other accredited educational institution or scientific research institution in the United States; and
the individual has not claimed benefits under Article 19 for more than three years in the aggregate.
A student, business apprentice or trainee who is, or was immediately before visiting a Contracting State, a resident of the other Contracting State and who is present in the first- mentioned Contracting State solely for the purpose of his education, training or obtaining special technical experience shall be exempt from tax in that Contracting State with respect to:
payments received from abroad for the purpose of his maintenance, education, study, research or training;
grants or awards from a government, scientific, educational or other tax-exempt organization; and
income from personal services performed in that Contracting State in an amount not in excess of 5,000 United States dollars or its equivalent in Chinese yuan for any taxable year.
The benefits provided under this Article shall extend only for such period of time as is reasonably necessary to complete the education or training.
本站一位作者以 F-2 身份入境美国，后来转成 F-1 读书，用学校提供的软件报税时发现无法 claim 这一条 treaty 。根据读者 Andy F 的查找，IRS 在 2002 年对此的解释如下：
Individuals who first enter the U.S. as an F-2 or H-4 are NOT eligible to claim the tax treaty benefit for students as they did not enter the U.S. for the purpose of being a student. The Treasury Dept is very specific about China in particular.
In general, persons who change immigration status from dependent to principal are not eligible for tax treaty benefits UNLESS the change to principal occurs within two months from the original arrival in the U.S. The IRS maintains that it is the PURPOSE for original arrival in the U.S. that determines treaty eligibility. Therefore, if someone changes purposes (goes from dependent to student, for example) they cannot benefit from tax treaty exemptions. AND, in the case of an F-2 who has been in the U.S. for a year or so, passes the TOEFL and goes home for the summer to apply for an F-1 visa and returns that fall, the IRS still says a resounding no to treaty benefits. This is because the NRA hasn’t been physically residing in the treaty country for at least a year prior to their arrival as a student in the U.S. Officially, they’re from “no country” for tax purposes, because they’re an NRA in the U.S., but U.S. tax law also has them as a nonresident in the home country. (There are a few exceptions to this, but mostly for diplomats who are considered tax residents of their home country no matter where they live or how long they’ve been away from home.)
This is because the NRA hasn’t been physically residing in the treaty country for at least a year prior to their arrival as a student in the U.S. Officially, they’re from “no country” for tax purposes, because they’re an NRA in the U.S., but U.S. tax law also has them as a nonresident in the home country.