Abstract: According to an analysis of the data of temperatures and R_o in the Zhanhua depression of the Shengli oilfield, the R_o=0.4% is determined to be the R_o threshold of hydrocarbon (including immature or low-maturity oil/gas) generation in the area, and the depth threshold and temperature threshold corresponding to the new R_o average~90℃ and~2250 m respectively. The related factors responsible for the relatively low R_o value are organic components, temperature, fluid pressure and burial depth. By comparison, the Bonan and Gubei sub-depressions of the Zhanhua depression have a high hydrocarbon generating potential, while the potential of hydrocarbon generation of the Fulin sub-depression is relatively low.