Abstract: Based on the systematic study on lithology, geochemical characteristics, reservoir characteristics and gas?bearing properties of Ordovician shale in Tarim basin, the paper considers that the Ordovician strata are extensively developed in this basin, in which organicrich shales include black carbonaceous shale, calcareous and siliceous shale. These shales are mainly found in Saergan formation ( 7~22 m in thickness) in the western Tarim basin and Heituao formation (40~60 m in thickness) in the eastern Tarim basin. The kerogen type of Saergan formation is Type Ⅰ and Ⅱ and that of Heituao formation is Type Ⅲ, all of which are good?high quality source rocks with the thermal evolution degree of high?matured to over?matured stage. The shale is dominated by quartz, the clay minerals are dominated by illite, the pores by mesopores and macropores with developed microfissures, and the brittle mineral content of the shale is high. Detrital minerals of the shale have good adsorption property. The gas content of downhole samples shows a positive correlation to organic carbon content, but the correlation of outcrop samples is not obvious due to weathering. The selected Middle?Lower Ordovician shale gas areas are located in the eastern Tarim basin with an area of about 1 582 km2, in Weili county with an area of about 1 058 km2, respectively. The estimated oil and gas reserves amount to 17 814×108 m3