Abstract: Ordovician reservoirs in the Tahe Oil field are dominated by fracture and vug,and have experienced stages of deformation.They have the same features as those in the northern Tarim Basin.1)Periods of karst effect.Caledonian paleostructure and karst palaeogeomorphology provided pathways for hydrocarbon migration and room for reservoir formation.2)The reservoir and cap combination in Ordovician itself worked as the most important combination for Ordovician reservoir.3)Karst unconformities offered ways for regional migration,and formed migration system together with fractures and fissures.4)Reserve conditions after accumulation controlled the distribution of ancient reservoir.Petroleum accumulated in the late stage mainly enriched in the higher locations.5)Accumulation started in the late Caledonian,and came across stages of filling adjustment.