Abstract: Chang 9 member of Yanchang formation in Honghe oilfield is characterized by low-middle porosity,super low-low permeability,small effective flow pore throat,low production and low recovery degree.Based on the core analysis data,combining with the normal section and scanning electron microscope data,the pore throat characteristics of the reservoir were studied and evaluated by using the mercury injection data as the key point.The results indicate the medium-thin throat of Chang 9 reservoir plays an important role in improving reservoir physical properties,while the micropore has little contribution to the permeability.The main contribution to permeability is the medium-thin throat which has a small proportion,which is of better sealing and permeability properties,and it is an important way to solve the problem of low recovery degree and poor water injection effect.