Abstract: The micro?pore structures and throat distribution of Chang6-Chang8 reservoirs of Yanchang formation in Fuxian exploration area of Yishan slope in Ordos basin are described in detail by means of constant speed mercury injection test, crude oil boundary layer test and fractal geometry method, and the control effect of micro?pore structure features on the percolation capacity is quantitatively characterized.Result shows that the sandstone reservoirs of Chang6-Chang8 members in this area are characterized by big pores and fine throats with strongly curved pore throat and size disparity, and dominated by distribution patterns of single?peak positive skewness and double?peak coarse skewness, for which the size and distribution of the throat radius could be decisive factor controlling the low?permeability reservoir’s fluid flow capacity. Also, they have good fractal geometry structures, and the sedimentary environment and diagenetic differences allow the reser?voirs to be of multi?fractal properties, while crude oil adsorption layer thickness in the extra?low permeability reservoirs accounts for 15%~23% of pore volume, and it is the formation of crude oil adsorption layer that could make the reservoir percolation capacity become poor