Abstract: The carbon-boron binary alloying layer was prepared on the surface of 45 steel by laser alloying process. The process was optimized by orthogonal test, and the microstructure and properties of alloying layer under the optimal process were studied. The results show that the optimal process obtained by orthogonal test included laser power of 2.2 kW, scanning speed of 500 mm·min^-1, overlap rate of 40%, and mass ratio of boron and carbon powder of 6.0:3.5. The alloying layer prepared under the optimal process was composed of Fe₃C, Fe₂B, FeB and γ- (Fe, C) phases, and consisted of alloying zone and heat affected zone. The microstructure of alloying zone was mainly columnar and cellular crystals, with a thickness of about 600 μm and an average hardness of 879 HV. The microstructure of heat affected zone was composed of acicular martensite and retained austenite, and its grains gradually became smaller from the matrix to the alloying zone. The thickness of heat affected zone was about 450 μm, and the hardness presented gradient distribution between 220-768 HV; The friction coefficient of alloying layer sample was about 0.466 6 and the wear rate was 0.455 3×10^-14 m³·N^-1·m^-1; compared with 45 steel matrix sample, the wear resistance was greatly improved.