To accurately obtain the flow and temperature field in mechanical seals and investigate the key influencing factors, a numerical analysis of flow and heat transfer in a contact mechanical seal with high-sealing pressure, high-operating temperature, and high-rotational speed is presented. A three-dimensional (3D) computational model consisting of seal rings, surrounding flushing fluid, and other seal components is constructed. fluent, a commercial computational fluid dynamics (CFD) software, is used to solve the 3D fluid–solid coupling model. Frictional heat, stirred heat, and convection coefficients are focused on in this study to ensure the reliability of the numerical results. The flow field and temperature distributions of the mechanical seal are presented, and the influence of different flushing fluid temperatures, flushing flow rates, and thermal conductivities of the seal rings on heat transfer is discussed. The results show that the stirred heat (accounting for about 10% of the frictional heat in the present mechanical seal) cannot be ignored for high-parameter mechanical seals. The flushing parameters can only influence temperature magnitudes on the seal rings but have minimal effects on the temperature gradients, which, however, can be well improved by adjusting the thermal conductivities of the seal rings.