A suit of lacustrine source rocks are developed in volcanic deposits in the Shangkuli Formation of the Cretaceous. However, it is poor to understand the characteristics of source rocks due to the low degree of exploration, thus the exploration is severely constrained in this area. Based on the geochemical analysis, the analytic technique of GC and GC-MS, combined with the characteristics of solvable organic matter and biomarkers of the source rocks, the authors discussed the depositional environment, the derivation of the matrix and the maturity characteristics of the organic material of the Shangkuli Formation in Cretaceous. The results show that the organic matter mainly belongs to type Ⅱ1 kerogen, whose abundance is relatively high; it was formed in reductive surrounding where was deep-lake; the hydrocarbon is characterized by mixed-source of organic matter. The thermal evolution of source rocks had reached maturation stage.