Abstract: The good source rocks discovered in Yangye formation of the Middle Jurassic in Jianggalesayi area of southeast depression in Tarim basin are dominated by lacustrine mudstone, with thickness of about 288 m, high organic matter abundance, and characterized by TOC of generally greater than 2.0%, hydrocarbon?generating potential of over 2.0 mg/g, kerogen types of II and III, as well as hydrocarbon?generating rate of 300 mg/g·TOC by high temperature and pressure simulation experiment. It is confirmed that the lacustrine source rocks of Yangye formation in the low mature?matured thermal evolution stages are distributed in south?central part of Washixia sag, with good hydrocarbon generating conditions, and certainly, it will be of a bright prospects for petroleum exploration