A numerical simulation was performed to study the natural convection and heat transfer of fluid contained in a rectangular cavity influenced by the different positions of thermal walls.The partial part of the left side wall was set at a high constant temperature and the partial part of the right side wall was set at a low constant temperature.The other parts of the side walls and the top and bottom of the cavity were thermally insulated.Under the conditions of symmetrical or a symmetrical location of thermal walls,the flow and temperature fields and the average Nusselt number of thermal walls were analyzed under different Rayleigh numbers.The results were obtained with Rayleigh numbers between 10³ and 10⁶.The heat transfer rate is high at the middle part of thermal walls in symmetrical case and at the middle-top part in asymmetrical case.