Abstract: Hanilcatam Ordovician reservoir in Tabei uplift of Tarim basin has long been considered as a secondary sag and hydrocarbon-generating sag of marine oil for its low tectonic location with the depth of 6500~8000m now, that constrained the petroleum exploration in this area. Through the structural interpretation and restoration of subsidence history, it was discoverd that during Caledonian-Early Hercynian it was belonged to the slope of Lunan great buried hill, which became a subsiding structural unit since Carboniferous. Carbonates in the Yijianfang Formation and Yingshan Formation of Ordovician experienced multi-stage karstification and developed weathering karst cavern reservoirs. The newest drilling data and geochemical features indicated that it was not hydrocarbon-generating sag during the deposition of Ordovician, with no source rock developed. The hydrocarbon in the reservoirs of Hanilcatam and the north area derived from Middle-Upper Ordovician source rocks in South West Manjiaer sag. The analyzing of oil and gas reservoirs indicated that Hanilcatam pools accumulated at the stage of Late Hercynian; the north tectonic uplifts before the sedimentation of Triassic led to local damage and degradation of the hydrocarbon in Ordovician reservoir. Since the deposition of Triassic beds, Ordovician reservoirs experienced continuous deepening process, with cover continual thickening and preservation of reservoir configuration, Hanilcatam area was an old petroleum system therefore. The analysis of hydrocarbon accumulation condition showed that there have superior hydrocarbon accumulation condition and great geological configuration. Ordovician carbonate karst reservoir distributed widely, which located in the favorable migration path to the high paleo-uplift, with the characteristics of widely distributed and quasi-layerd accumulation.