Abstract: Based on the comparison experiments of a large number of surface, downhole and subsurface samples, the authors pointed out that surface weathering mainly has serious impacts on the organic matter abundance of hydrocarbon surce rocks, and the weathering degrees of samples with different lithology and different parameters are significantly different. In this paper, some weathering correction coefficients of organic carbon for the surface samples from the Qinghai Tibet Plateau are suggested. In is indicated that the effects on soluble organic matter such as bitumen "A", total hydrocarbon, pyrolysis free hydrocarbon S₁ and cracking hydrocarbon S₂ as well as pyrolysis IH are great, thus they are difficult to be corrected.Also, some primary control factors about the impacts of surface weathering on organic matter abundance are discussed.