Abstract: The goal of the research on Cr5Mo heat-resistant steel welded with P5 electrode was to determine the effect of preheating and PWHT on microstructures and properties of fusion zone,the residual stress distribution and the elevated temperature enduring tensile properties in welded joints and the pattern of carbon migration in fusion zone,The results of the research are as follows:the optimum preheating temperature for welding dissimilar steels was about 300℃,preheating had little effect on the distribution of residual stress; the high temperature post-weld tempering did not relieve or reduce residual stress but did redistribute residual stress;there was some carbon migration in weld joint but it was not significant, during 500~600℃,the enduring strength of welded joint was equivalant of base metal;preheating could improve the enduring strength but PWFHT could not.