Abstract: The surface thermo-elastic deformations of a hydrostatic mechanical seal in reactor coolant pumps play an important role on sealing performance when they operate at high pressures and high speeds. A thermo-elasto-hydrostatic coupling model is established for such a seal with a double tapered face forming a convergent gap by considering the variations of dynamic viscosity of sealed fluid with fluid pressure and temperature, heat transfer between lubrication film and seal rings and the deformation of end faces. The governing equations for fluid film pressure and temperature are numerically solved by using finite difference method, and the thermal-mechanical deformations are simulated by using finite element method. The thermal-fluid-solid coupled analyses are carried out. The effects of thermo-elastic deformation on sealing are studied. A comparison of sealing performance between the two types of such seals with one or double tapered surface are analyzed. The results show that a double tapered hydrostatic mechanical seal has higher stability than that of a one tapered hydrostatic mechanical seal. The outlet cone has greater influence on leakage rate than that of the inlet cone, but it has less effect on the opening force than that of the inlet cone. The film stiffness to leakage ratio becomes larger when the inlet cone face width ratio equals to 0.05. The surface temperature distribution of a double tapered face seal ias more uniform than that of a one tapered face seal.