Abstract: Using parameters of bitumen A, hydrocarbon content, hydrogen/carbon, atomic ratio, macer als and vitrinitc reflectance, a systematic correlation on the parameters from the wells Nan 6 and Nan 11 has been made. The two wells are located within the same faulted depression and have expe rienced similiar sedimentation but different in the thickness of the overlying sequences. It is revealed that a secondary evolution of hydrocarbon generation did occur in the Carboniferous -Permian coal series within the area. Preliminarily the depth for the hydrocarbon generation threshold is defined at 3400m, and the initial expulsion at 4000m deep. The author believes that what mentioned above can provide scientific basis for the explorations of gas (oil) pools derived from the secondary evolu tion of coal series.