Abstract: Cold metal transfer（ CMT） welding technology was used to surfacing high Cr alloy steel on Q345 steel,so as to strengthen the surface of Q345. The results showed that the method of CMT surfacing high Cr alloy steel on the surface of Q345 steel was feasible,and the weld was well combined with the matrix without obvious cracks. The microstructure of the substrate was mainly ferrite and pearlite,while the structure of surfacing layer was mainly martensite and residual austenite. CMT welding had low heat input,the heat affected area was small,so dilution rate of the substrate at the interface was low. The average hardness of surfacing layer was 490 HV0. 2,while the average hardness of the substrate was 182 HV0.2. Impact absorbed energy of the composite plate was 35 J. The main fracture morphology was the tearing edge and the crack bifurcation was found at the interface between the substrate and the surfacing layer.