There are outcropping Upper Sinian carbonate rocks in the northwestern margin of Tarim basin.Based on field investigation and experimental analysis of outcrop samples,four types of carbonate reservoirs are recognized and the characteristics of them are as follows: (a) Paleokarst reservoirs,in which solution pores and caves are general and various,widely develop in the weathering crust on the top of the Upper Sinian strata.They are the best reservoirs in this area.(b) Microbial dolostone reservoirs,in which various microfabric-associated solution pores are common,develop in the middle and upper parts of the Upper Sinian strata.They are a sort of deeply-buried tight reservoirs with low porosity and extremely low permeability.(c) Crystalline dolostone reservoirs,in which intercrystal and solution pores are typical,are characteristic of low porosity and low permeability and are locally distributed.(d) Thermal-altered dolostone reservoirs,in which hydrothermal dissolved pores and caves or residual intercrystal pores are common,are distributed only in some local area (such as Xiaoerbulake) where great faults develop in deep.