Mixed sedimentation of terrigenous clastic and carbonate is a sedimentary phenomena has special sedimentation mechanism and significant. It is developed extensively in the Upper Ordovician Sangtamu Formation of the Tarim basin. This paper studied the mixed sedimentation in this area based on regional geological data, well logging data, observation of wells cores, indoor sample analysis. The results show that the research area is characterized by interactive sediments of terrigenous clastic and carbonate on the microscopic level, called “mixed sedimentary rock”. And in the macro performance of the mixed sequence composed of terrigenous clastic rock, carbonate rock and mixed sedimentary rock. The mixed sequence is divided into 5 types of gradient, mutationI, mutationII, compoundI, compoundII. Mixed sedimentary environments are occurrence of sedimentary facies such as mixed tidal flat, mixed platform, mixed platform margin, mixed shelf. Combination of tectonic setting and guided by the sedimentary principle, this paper proposed a mixed sedimentation model of the Upper Ordovician Sangtamu Formation in Tarim basin. And further summarized and discussed controlling factors of the mixed sedimentation.