The research on fracture has important significance to oil development, irrigation works and underground space utilization. While the geometrical form of actual roughness of fracture surface will influence the specification of liquid flowing and conduction capability of fracture, cubic law is failed to be executed. Based on the standard section outline curve of JRC, various researches on different JRC regulation were performed via reverses digital modeling method. The result showed that when a consistent pressure differential acts on both sides of fractures owning different roughness, liquid flow is gradually reduced along with the increase of joint roughness , the differential pressure on both sides will be gradually increased with the increase of surface roughness when the flow that running into various certain surfaces is fixed. Comparing simulation result with experimental one, the relationship curve between fracture mechanical width and flow showed obvious non-linear feature, two lines match well and accord with logarithmic relation.