By melting on the martensite low carbon Hardox 400 steel alloyed by powder weld wire EnDOtec DO*33, the microstructure of surface coating obtained by electron beam treatment (EBT) is investigated by the methods of transmission electron microscopy. The results show that due to the application of electron beam treatment, lots of submicro and nanodisperce structure containing the carbides of the Fe, Cr and Nb are formed, and the cementite is the main phase component, which is beneficial to the improvement of the mechanical properties. Therefore, the application of EBT is an effective method to increase the structural homogeneity and to refine the phase grains.