Abstract: China low activation martensitic steel used for fusion reactor was welded by laser welding process,and followed by the post-welding heat treatment(PWHT) at 740℃ for 1 h.The characteristics of microstructure and mechanical properties of welded joints were analyzed before and after PWHT,respectively.The results show that the weld seam with good formation and without defects has been obtained.In as-welded condition,the microstructure obtained in weld metal is quench hardening lath martensite with high percentage of delta ferrite.The hardness value of full quenched zone is up to 545 HV due to its fine lath martensie besides of small percentage of delta ferrite.After the PWHT,the lath martensite,in the weld metal and the completely quenching zone,transformed into tempered martensite and tempered sorbite with dispersed carbides,which decreased the hardenability of the weld joint obviously,and the highest microhardness was only 15% higher than that of the base material.The tensile strength of weld joint was higher than the base material both before and after the PWHT.Although the PWHT could decrease the strength of the weld joint,it was also about 98% of the original base material.