Ram is a functional part of great importance to a CNC planer type milling machine. The overlarge thermal deformation of the ram will reduce the working accuracy of the machine. By applying theory of thermo elasticity and finite element method (FEM), the thermal characteristics analysis of the ram was completed, and the finite element equation (FEE) of deformation caused by thermal mechanical coupled was established. Aimed at the problems existed in actual machining, the finite element model (FEM) of the ram was established, the heat source and the way of heat transfer and boundary conditions were ensured, and the thermal characteristics and thermal-mechanical coupled analysis of ram were finished by ANSYS Workbench software. The temperature field distribution and thermal deformation were obtained by computation, which provide theoretical support for improvement during the designing of the ram of CNC machine.