Abstract: The maturity of organic matter in sedimentary rocks is the accumulating effects of thermal evolution in burial history. Such an accumulated effect could be expressed by time-temperature-index (TTI) or vitrinite reflectance (R°), The greatest burial depth and the original thickness of sedimentary sequences can be obtained by the method of reversion, once the TTI (or R°) and the burial history in certain areas are available. The precision of this method depends on the parameters, such as geothermics and thickness of sedimentary sequences, TTI,R°,etc.. If upliftings and sudsidings take place,you should make corrections both on the depth and the thermal effects of time-temperature.