The serious mechanical seal leakage is found for the hydraulic turbine of a diesel hydrogenation modification device during the test run. The hydraulic turbine uses the rotating tandem mechanical seal and the auxiliary sealing system with PLAN 53B irrigation scheme based on API standard. Through the analysis on the mechanical seal structure and the auxiliary flushing system, the main causes of the mechanical seal leakage were pointed out, which was that the pump ring head of the mechanical seal was insufficient and the heat exchanger pipe resistance was too large, the fluctuation of the rotary series sealing ring affected the dynamic discharge of friction heat and medium transfer heat, and the spacer fluid was vaporized at high temperature. Through the transformation of heat exchanger and pump ring, the temperature in the liquid separation chamber and the sealing cavity is reduced. By transforming the rotary series sealing into double end face static seal, the heat exchange efficiency is improved. By using high boiling point spacer fluid, the problem of gasification of spacer fluid is solved. The transformed mechanical seal achieves a better sealing effect, and the load of hydraulic turbine motor is reduced.