In order to study the effect of preheating temperature on post weld residual stress and mechanical properties of SA387 material,four different preheating temperatures were used to weld the test plates respectively.The residual stress of the test plate after welding was measured.It is found that the welding residual stress decreases first and then increases with the increase of preheating temperature.Through mechanical property test and microstructure observation,it is found that preheating temperature has a great influence on the mechanical properties of the material.The tensile strength and yield strength of the material decrease with the increase of preheating temperature,and the toughness first decreases and then increases with the increase of preheating temperature.Based on the test results of welding residual stress and material mechanical properties,it is suggested that the preheating temperature of SA387 Gr11 Cl2 should be 265-290℃.