Abstract: Through analysis of rock thin section, pore throat test, oil-water phase permeability test, initiation pressure gradient test and other core experiments as well as well logging and borehole logging data, the characteristics of Chang 9 reservoir of Yanchang formation in Honghe oilfield was studied. The results show that the content of cuttings is slightly higher in high porosity and permeability reservoirs, and the content of mica and clay is lower. The pore-throat structure of mercury injection analysis is obviously better than that of low pore-permeability section, and the relative permeability value of the phase permeability curve is obviously higher than that of the low permeability reservoir. Under the same water saturation condition, the oil phase permeability is higher and the water yield is more than 10% lower. The micro throat radius is greater than 1.2μm and the starting pressure gradient is less than 0.06 MPa/m. The high porosity and permeability reservoirs are mainly caused by the large-scale dissolution in the middle and late diagenesis, which improves the local reservoir space and the seepage channel in Chang 9 reservoir and the reservoirs with high porosity and permeability is distributed in the middle and lower part of Chang 912 reservoir.