The Mangya depression, located in the western Qaidam Basin, is one of the main oil-bearing units in the Qinghai oilfield. Two vertical distribution styles have been found after the study of the Tertiary vitrinite reflectivity (R o). Firstly, a linear correlation between R o and depth is conspicuous, and it is clear that such distinct relation exits in the center of the depression, which shows stability of the sedimentary environment, the sources of sediments and the structural activities. Secondly, it is found that thrusting and superposition are developed according to the dextral-stepped arrangement of R o and the depth in the cross plots. What is more, by calculating the denuded stratum thickness in the work area with the method named EASY%R o, the main structure should occur along Ganchaigou-Youquanzi. However, the present landform shows that the main peak of the Yingxiongling is the ridge axis. This ostensible appearance can be well explained if we take the denudation in this area with a thickness of 3600~3750 m into account. It is also found that most of the oilfields distribute along denuded gradient zones. These results are important for the exploration and development of the Qaidam Basin.