Abstract: The microstructure and properties of iron and steel materials can be improved by electron beam scanning surface alloying. In this paper, the surface of 45 steel is treated by cladding alloy by plasma spraying technology and electron beam scanning technique. The effect of electron beam scanning on the strengthened layer was investigated. The results show that 45 steel treated by surface alloying, the surface can be divided into alloying zone, heat affected zone and the base zone. The microstructure of the alloying zone was acicular martensite and tungsten carbide particles, the microhardness is 1 250 HV, which was 5 times of the substrate; the microstructure of the heat affected zone is acicular martensite and ferrite. The microhardness was 860 HV, which was 3 times of the substrate. The microstructure of the substrate was pearlite and ferrite. The technological parameters of the electron beam had great influence on microstructure and hardness of the strengthened layer. The thickness of the strengthened layer increased with the increase of the beam power, and decreased with the increase of the scanning speed.