The source rock of Upper Permian Rejuechaka Formation in Laxiongcuo area of Qiangtang Basin is characterized by dark gray-ash black and thin-very thin layers. An analysis of organic matter shows that total organic carbon content varies between 0.31% and 0.72% in the source rock, mainly reaching a poor-medium standard. The organic matter mainly belongs to II₂ type. Parent material of the organic matter was derived from a reducing environment with considerable salinity, and mainly came from plankton, algae, pilze with the mixture of a small amount of higher plants. The thermal evolution degree reaches high maturity stage. The discovery of the source rock further suggests that Paleozoic source rock has good hydrocarbon generating potential. The result obtained by the authors provides basic geological information for the assessment of oil and gas resources in Qiangtang Basin.