Abstract: This paper applies the mathematics model of the overthrust thermal effect described by Angevine, et al. ( 1983 ) to study the thermal history of the Permian source rocks in the Klamai-Ulh overthrust belt. Based on the thermal maturity indexes, such as the vitrinite reflectance of samples collected from different structure position, the paleotemperature is recovered and thermal maturity evolution of organic matters simulated. The thermal modeling demonstrates that the maturation of the source rock located at the lower part of overthrust stage increased owing to the affection of thermal conduct deriving from high geotemperature of the overthrust-sheet bottom, so the source rock of Permian reached the stage of oil-generation peak at the beginning of Jurassic. Howerer, the velocity of the source-rock maturation of the same age in the upper wall slowed up due to quickly cooling, and the maturity was almost not elevated in the post-overthrust stage. This mold of the overthrust thermal effect canbe applied to not only simple overthrust, but also multiple thrust. In this paper Zayier Overthrust Belt is studied as an example of multiple thrust. As its overthrust sheet is very thick and the overthrust thermal effect rather strong, the velocity ef thermal maturation becomes rather quick and source rocks come into overmaturation quickly.