明白了。还有一个小小疑惑：

“Another tax benefit if you file 1040 is you can claim child tax credit (if you have at least one child and income under certain threshold).“

如果claim tax treaty, Federal tax 应该100%退，还有必要claim child tax credit 吗？

另外关于州税，是不是各个州规定不同，我搬来PA,这里的朋友说PA的州税不能 covered by tax treaty.

谢谢。