The thermal characteristics of the mechanical seal of hot oil pump under different operating conditions and structure parameters were studied in order to prevent mechanical seal invalidation. The three-dimensional thermalforce coupling model consisted of the rotary ring, stationary ring and stationary seat of the mechanical seal was established by using the finite element software ANSYS, and the interpolating function of heat flux was calculated by using MATLAB. Through loading on every element by UDF, the heat flux on every node was calculated, and the thermal characteristics and interface temperature rise of mechanical seal were analyzed under different rotary speeds, materials and related structural parameters. The analysis results show that the temperature in the interface of the mechanical seal is highest in the process of operation. The interface heat is mainly conducted by the rotary ring, and changing the O-ring bearing position can optimize the temperature rise of mechanical seal. Along the increasing of the interface width and the load factor, the interface temperature rise is all increased. The interface of mechanical seal has no phrase change under stable running state.