Based on drilling core, logging curve, petrographic thin section, SEM(scanning lectronic microscope), physical property and mercury penetration data, the characteristics of Mesozoic reservoirs in the southwest of the Zhidan district in the Ordos basin have been studied systematically. It indicates that the reservoirs of Triassic and Jurassic not only distribute widely but also possess great thickness. The Yanchang and Yan'an formations are mainly delta front sand-bodies, except that Yan10 is braid river sand-bodies. The Yanchang formation is fine and extremely fine-grained arkose, while the Yan'an formation is mesograin and meso-chondro-grain sub-lithic arkose, feldspar sandstones, and a little gritstones of feldspar-quartz and of gravel. Remnant inter-granular pore and solution pore are the dominant accumulation space. The reservoirs of the Yan'an formation have good pore structure and better physical properties than Yanchang's. They are middle-pore and middle-permeability reservoirs, and some of them are highly permeable. The Yangchang formation has the reservoirs of middle-low-pore, low-permeability, or low-pore, low-permeability. The better reservoirs are developed in Jurassic Yan8-10 and Triassic Chang 2 oil-bearing group, followed by the Chang 6.