Abstract: The lubricant temperature at the outlet of acceasory gearbox is an important parameter required in designing many kinds of aeroengine components. The temperature and its field distribution and the heat dissipation through gearbox case are conditional on each other in computation, thus making the computation much more difficult. A theoretical computation model is deduced, and the process to compute the heat dissipation by a finite element software is studied. In addition, an iterative method is introduced to solve the problem of the temperature field that is unknown. Then, the temperature field distribution of the accessory gearbox and the temperature at its outlet are both given. It is proved that the computed results comply with the safety-oriented empirical valves. The software we developed on the basis of the result database of ANSYS to compute the heat dissipation is available to the heat dissipation of complicated shapes and boundary conditions as well as that of anisotropic thermal conductors. The error computed by the program is less than 1 % in comparison with theoretical calculation.