Laser welding experiment was done on the reduced activation martensitc steel which is used in fusion reactor,the microstructure and mechanical properties of the welding joint were tested in this paper. The results show that the joints with good quality can be obtained by laser welding. The microstructure in weld is lath martensite,while the heat affect zone (HAZ) comprised coarse grain zone and fine grain zone. The structure of coarse grain zone is coarse pearlite and a mixed structure which comprises fine pearlite and ferrite in fine grain zone. The hardness of the weld was about 530 HV,while minimum hardness was about 220 HV in HAZ. The tensile strength of the weld joint reached 775 MPa.