There is an abnormal matter thermal evolution for Middle Jurassic coal beds and shale in the Chaidaer Mine of the Muli Basin, Qinghai Province. The source rocks in the upper part of the Middle Jurassic are highly mature (R0=1. 31%-1. 58%), while the source rocks in the lower part of the Middle Jurassic are only in a mature stage (R0 = 0. 79%-1. 18%). Hydrothermal alteration caused such abnormal thermal evolution, as is proved by the modeling of the burial histo- ry and thermal history. As the modeling result shows, both the upper part and lower part of the Middle Jurassic entered the petroleum-generating threshold and began to generate oil and gas in Late Jurassic time and reached the mature stage when petroleum was generated in large amount. Subsurface hydrothermal solutions flowed up along the deep fault F0 at the end of the Cretaceous, which increased the maturity of organic matter in the upper part of Middle Jurassic rapidly during 5 Ma. Then the source rocks in the upper part of the Middle Jurassic became highly mature and condensate oil and wet gas began to be generated.