Abstract: The Junggar basin in Jimsar depression X group’s lithology give priority to fine siltstone, micritic dolomite and transition rocks, the average porosity is 9.17%, the average permeability is 0.15 mD, belongs to low porosity, low permeability reservoir. With the method of conventional high pressure mercury injection experiment we find out that, Reservoir microscopic pore structure change is poor; with the method of Constant velocity mercury injection experiment learned that, Reservoir percolation ability is mainly composed of throat radius distribution and pore throat radius ratio distribution.