Previous studies suggest that the maturation of Permian hydrocarbon source rocks reached the peak of hydrocarbon generation very early,which inconsistent with the conclusion about oil accumulating stages. To reacquaint the source rock thermal evolution history,the thermal history and the suppression of overpressure on organic matter maturation were analyzed in detail. The results show that Junggar Basin experienced rapid cooling process in Middle Permian to Early Jurassic due to the transformation of tectonic thermal regime. All aspects of organic matter maturation were retarded by overpressure. The degree of suppression increased with the pressure coefficient increases and reached the limit(Ro values lower about 0.6%) when the pressure coefficient reached the maximum value. Using the overpressure factor,which was associated with the pressure coefficient,to regulate the chemical reaction frequency factor in Easy% Ro model can effectively reflect the retard characteristics of Ro values. Then,based on the improvement of Easy% Ro model,maturation histories of main source rocks in Pen 1 west sag and Shawan sag were modeled. The modeled results show the main stage of oil generation of P2+3w source rocks was the Cretaceous,and J1b source rocks are still in the main stage of oil generation. This result was obviously later than the time modeled by traditional model,which is in favor to deep petroleum accumulated rapidly in later period.