Abstract: Ermahu depression is located in a secondary structural unit in the west of the northern depression of Wuwei Basin. The Carboniferous coal measure strata are developed in this depression, and there is a certain potential for CBM exploration. However, for a long time, the structural evolution process and the maturity history of organic matter in this depression have not been studied. In this paper, the structural evolution and thermal history of this area have been studied by using the balanced profile technique and reservoir forming simulation technique. The results show that:①Erma Lake depression is a compound fault depression controlled by several NE trending normal faults; ②The depression experienced four stages: Carboniferous-Permian rifting stage, Triassic-Early-Middle Jurassic uplifting and denudation stage, Late Jurassic-Early Cretaceous secondary rifting stage and Tertiary-Quaternary depression stage; ③The thermal evolution of the Carboniferous source rocks in the Ermahu Sag is relatively high. The Carboniferous source rocks entered the stage of oil generation at the end of Permian, and entered the stage of gas generation at the end of Triassic, and are currently in the stage of high maturity-over-maturity.