With the advent of bottleneck of the conventional oil and gas resource exploration，tight oil and gas reservoirs are becoming more and more important for exploration and development. In order to further reveal the micro pore structure characteristics and their influences on reservoirs seepage，conventional mercury injection and constant velocity mercury injection method were applied to analyze comprehensively pore structures of tight reservoir in the Lucaogou Formation of Jimsar sag in Junggar Basin combining with casting thin section analysis，scan electron microscope observation and other means. The experimental results indicate that under dissolution and cementation conditions，the main pore type in the research area is characterized by intragranular dissolved pore，half filling pole，intergranular dissolved pore，intercrystal pore and intracrystal pore. Five types of the reservoirs were divided and evaluated respectively，on the basis of the conventional mercury injection curve distribution and its morphology，the porosity and permeability and the parameters characterizing pore throat size，sorting and connectivity. The configuration between pore throat and pore and the pore throat radius of the reservoir in the study area are different from those of conventional reservoir. Reservoir seepage is controlled by both pore throat radius distribution and pore-throat ratio distribution. The bimodal distribution of pore-throat ratio indicates a combination of two types of pores in the reservoir，which suggests a potential target that should be emphatically developed in this area.