Abstract: The optimized laser welding process was used to weld the 6mm thick CLF-1 steel and subsequent weld tempering heat treatment. The sample were characterized by electron channel contrast and electron backscatter diffraction, and the microstructure evolution of as-weld and tempered CLF-1 steel was studied. The results show that as-weld area mainly consist of α′-Fe single phase dislocation martensite structure, transformation martensite follows KS and NW orientation relationship; After post weld heat treatment, M23C6 phase precipitated in the interior and interface of martensite variant respectively. Post weld heat treatment can effectively reduced the orientation difference in the interior of martensite variant, but it have little effect on the martensite phase. The microhardness test results show that the microhardness of the as-weld area of CLF-1 steel is 358HV0.2 and the microhardness of the weld significantly reduce to 258HV0.2 after post weld heat treatment. At last, a good stress removal index can be obtained by tempering treatment.