Abstract: The porosity characteristics of reservoir play an important role in the evaluation of gas-bearing and the production capacity of shale gas.In order to study the pore characteristics of shale gas reservoir in Shanxi formation of Yanchang exploration area, this paper integrates various technologies, such as observations of argon ion etching-polishing emission scanning electron microscopy, core observation, thin section, X-ray diffraction analysis, nuclear magnetic resonance and mercury injection to explore the pore types and pore structures detailed.The results show that the shale gas reservoir in Shanxi formation are dominated by clay mineraland quartz, it contain higher clay mineral and clay mineral content have larger variation from 43.5% to 98%.The reservoir develops a large number of micro-fractures and micro-pores.The pore size of reservoir ranging from 0.5 μm to 20 μm, pores are dominated by tiny pores, throat is small and unevenly distributed and pore throat sorting characteristic is poor.The micro-fracture of mud shale in the Shanxi formation is extremely developedobserved under the microscopeand the area density of crack can measure up 108.8/m, these pores and fracturesform a network structure are main channel for shale gas seepage and provides storage space for shale gas.Total organic carbon is higher, the number of organic pores will increase accordingly, and decrease in detritus content will reduce the degree of extrusion of organic matter, which propitious to the preservation of organic pores.Higher thermal evolution can increase organic pores under the effect of organic hydrocarbon generation and gas expansion, and clay minerals an form micro-fractures during dehydration conversion.All of them have a promoting effect on pore development.