Thank you very much. I can tell that it has a crown stripe so I suspect that it is a Pallas's Leaf Warbler. But in "The BIRDS of HONG KONG and SOUTH CHINA", it said Yellow-Browed Warbler occasionally has a faint crown stripe, so I am not sure how to identify it. I have other photos show that it has yellow rump and it is very active too. So I think it is a Pallas's Leaf Warbler.