Abstract.. Based on observations of cores, rock sections, casting sections, logging data of Ordovician carbonate reservoirs in the Yubei area, Tarim Basin, reservoir space is dominated by cavities and fractures, and can be classified into four types, i. e. cav- ity-fracture type, fracture type, pore-cavity-fracture type and pore-cavity type. Specifically, reservoirs in the upper part of the Lower Ordovician Yingshan Formation are controlled by multi-period unconformities and mid- to high-angle fractures, while reservoirs in the lower Yingshan Formation and the Penglaiba Formation are closely related to dolomitization and development of interlayer low-angle fractures. Integrated analyses indicate that flank province of fault folded structures are favourable to development of cavity-fracture reservoirs in the lower part of the Lower Ordovician Yingshan Formation, while the east- west oriented fault zone through Well sbenghe 2 and the vicinity of the north-east oriented fault zone in the east part of Yu- bei area are favorable areas to prospect for pore-cavity dolostone reservoirs in the lower Yingshan Formation and the Pen glaiba Formation.