Based on the thin wall wet cylinder liner of a heavy-duty diesel engine, calculations are carried out on the three-dimensional temperature field by finite element method (FEM). The results show that the highest temperature of the cylinder liner is 229℃ in the top dead center. Combined with the special thermal boundary condition, the steady-state temperature field of the cylinder liner are calculated and the effect of different cylinder thickness on the thermal load are compared. The importance of involving the thermal load in the analysis cylinder deformation are underlined. All these provids theoretical directions and foundation for cylinder liner design.