Abstract：Permian hydrocarbon source rocks are an important potential hydrocarbon-generating sequence in the Turpan depression, northwestern China. Mainly based on the analytic data of dark mudstone on the outcrop sections, combined with the geochemical data from core samples of hydrocarbon source rocks, the trace geochemistry of mudstone is discussed in detail and the sedimentary environment of the source rocks is analysed by unsing the organic carbon content, organic matter types and saturated hydrocarbon chromatogram parameters of the source rocks. The studies demonstrate that the deposional environment was the weak reducing-reducing one. The terrigenous organisms predominate in the organic matter of the source rocks, and lower aquatic organisms are also present in large quantity. The hydrocarbon is the product of conversion of organic metter deposited in the reducing environment. The depression has a high genetic potential. The sedimentary zones with a strong reducing power and fairly deep water bodies are favorable sites for deposition of primary organic matter, where deposited organic matter can be buried and preserved in time. Therefore most hydrocarbon source rocks contain abundant organic matter and vice versa.