Abstract: Environmental wind will influence the working conditions of natural convection cooling tower.The velocity and temperature fields in the natural convection cooling tower of the HTGR residual heat removal system at different environmental wind velocities were numerically simulated.The results show that,if there is no wind baffle,the flow in the cooling tower is blocked when environmental wind velocity is higher than 6 m/s,residual heat can hardly be removed,and when wind velocity is higher than 9 m/s,the air even flow downwards in the tower,so wind baffle is very necessary.With the wind baffle installed,the cooling tower works well at the wind speed even higher than 9 m/s.The optimum baffle size and positions are also analyzed.