I came to US in 2010.3 as a visiting schorlar holding J1 visa.In 2011.7 I went back to China and change J1 to F1. Now I am a student. Recently, I received a letter from the tax offcie in my school telling that I am not eligible for tax treaty due to my changes from J1 to F1 status without properly re-establishing my residency requirement with China according to the Treasury Department guidelines. So what's this mean? And am I eligible for tax withholding for the first 5000$ income as student now? Thanks do much for your help.

You had J1 before F1. Even on J1 you are nonresident for two years. You should get tax treaty benefit.

I agree; you should get the treaty exemption for 2011.