Abstract: Leakage model for contact mechanical seals was established. Using fractal parameters characterizing surface topography and introducing the pressure flow rate factor reflecting actual rough surface on leakage passage, fractal expressions of average film thickness and pressure flow rate factor were derived, and leakage fractal model based on average film thickness and pressure flow rate factor was established. Influence factors of leakage rate for mechanical seal were analyzed by theoretical calculation, and two sets of B104a-70 mechanical seals tests were made on the self-designed mechanical seal testing device. Test sealant was 20 ℃ water. Test pressure was 0.5 MPa. Rotating speed was 2 900 r/min. Spring pressures were 0.15 MPa and 0.30 MPa. Results show that leakage rate decreased slightly with the increasing spring pressure, and it increased with the increasing sealant pressure and rotating speed, and end face was more coarser, the amplitude of increasing was more larger. Leakage rate decreased rapidly with the increasing fractal dimension or with the decreasing characteristic length scale when the surface was coarser, while leakage rate changed little when the surface was smoother. The theoretical calculated values of leakage rate were consistent with the experimental values well, especially in the normal wearing stage.