Austenite type surface coating was produced using pure Cr and Ni powders and slagging elements B and Si on 45# steel with light beam alloying. The effect of alloying process on appearance, microstructure and phase of alloying coating was investigated by SEM, EDS, X-ray diffraction, etc. The results show that appearance and microstructure of alloying coating are not only determined by heat input, but also relevant to dosage of slagging elements B and Si when dosage of alloying elements is invariable. Dosage of slagging elements B and Si has to be increased for good appearance of alloying coating while heat input is increased. Microstructure of alloying coating produced by low heat input is composed of the great mass ofγ(Fe,Ni) and a small quantity ofα(Fe2Cr) at γ(Fe,Ni) boundary while there isγ(Fe,Ni) + Cr2B eutectic at γ(Fe,Ni) boundary of alloying coating produced by high heat input.