Abstract: In Maling oilfield,8 samples of Chang 8 oil layers were selected for constant speed mercury injection experiment to make clear the microscopic structure of low permeability reservoir.The relationship between the permeability parameters was studied and the study results indicated in the case of small permeability change range,there was a good negative correlation between fractal dimension,pore throat radius ratio and permeability,while the representative parameters such as pore radius and tortuosity had no good correlation with permeability,which showed there may be no good correlation between the single parameter of low permeability reservoir and the change of physical properties.