Abstract: The characteristics of micro pore throat structure of tight oil reservoirs are the bottleneck in study of tight oil reservoir. It also holds the key to tight oil development. Take Chang 7 tight oil reservoir in An-83 block of Jiyuan oilfield in Ordos Basin for instance. Based on microscopic observation and mercury intrusion experiment, micro pore throat structure of the reservoir is brought under analysis. Microscopic observation indicate that the main types of pores in this zone are feldspar dissolution pore and intergranular pore, while the types of throat are mainly tortuous sheet shape, sheet shape and bundled tube. The intrusive mercury curves indicate that the expulsion pressure and median value pressure are relatively high, with the curves having a higher pitch of intermediate section and a low throat radius. Heterogeneity of pore throat structure is the main factor to determine the filtration characteristics and differences of tight oil reservoir. The analysis of the correlations between parameters and physical properties in three areas of pore distribution, pore sizes and pore connectivity indicate that the sorting coefficient in the parameters of pore distribution, the pore volume ratio in the parameters of pore sizes and the mercury withdrawal efficiency in the parameters of connectivity have the best correlations with the physical properties. As a result, the appropriate appraisal standards are established to classify tight oil reservoirs, helping appraise productivity of tight oil reservoirs and optimizing the relative measures.