Abstracts：The mixed siliciclastics and carbonate sedimentary system is developed extensively in eastern Qiangtang basin. Based on previous research results, the authors studied the diamictite and diamictic system, terrigenous clastic rock and carbonate rock by means of regional geological material analysis and inner sample analysis. The results show that the study area is characterized by interactive sediments of terrigenous clastic rock and carbonate rock at the microscopic level, called “mixed rock”, and that in the macroscopic performance there exists the mixed sequence composed of terrigenous clastic rock, carbonate rock and mixed rock. Mixed sedimentation resulted from facies mixing with minor source mixing and event mutation, which formed the sedimentary system of shore, carbonate gentle slope and tidal flat-lagoon. Combined with the tectonic setting and guided by the sedimentary principles, this paper proposes a mixed sedimentation model for the eastern part of the Qiangtang basin in Tibet.