I do not think this is a Pallas's Warbler, and feel that it looks more like a Yellow-rumped Warbler type or Gansu Leaf Warbler.
The head pattern looks very odd for Pallas's: the crown is not dark enough (showing little contrast with the mantle), the crown stipe is diffuse and dull (obviously duller than the supercilium), the eyestripe is poorly defined.
In addition the wing lacks sufficent contrast as the centres to the greater coverts and median coverts are not very dark and there little in the way of shadow below the greater covert wing bar.
On the left wing the central tertial has been replaced and show a dull, ill-defined tertial fringe, which is again at odds with Pallas's.
One feature which appears to favour Pallas's is the strong yellow tones to the front part of the supercilium.
I am not sure if the overall green tones are of importance for id, but would note that on tail shape it looks like an adult, and an adult would obviously be brighter than a first-winter at this time of year.
There is a good selection of Yellow-rumped and Pallas's Warbler at OBC images (just remember that the Himalayan Yellow-rumpeds have been split from the Chinese birds - they look quite different).
