With the rapid development of industry technology and continued increase of the degree of mechanization and automation, people pay more attention to hazard of parts wearing. It has a great economic significance that decrease grinding abrasion and increase mechanical wearing.Electromagnetic technology is applied to welding as a new welding method in recent years. The numerical analysis models of intermittent alternative magnetic field and its distribution are established at first time, and general control equation and boundary condition are presented, according to the characteristics of nonlinear, multi-factor, transient and strong coupling in the intermittent alternative magnetic field, by using non-electric quantity measuring techniques and finite-element analysis method. The general numerical simulation models of intermittent alternative magnetic field of plasma arc surfacing layer are constructed for the first time, which is suitable for calculating the distribution of intermittent alternative magnetic field. The models of distribution of intermittent alternative magnetic field have been validated by carrying out welding technology tests comprehensively. It is shown that the computed results are found to be in good agreement with the experimentally observed one or the precise analysis result.The applied intermittent alternative longitudinal magnetic field promotes arc revolution, changes plasma jet of arc column and radial distribution of density of arc, affects the heating and melting of base metal and formation of weld. The intermittent alternative transverse magnetic field has influence on the swing frequency of welding arc.Experience shows that the introduced magnetic field can give an effective intervention to the transition of droplet, flowing of molten bath metal, crystalline and nucleation of molten bath and the process of crystalline growth. The magnetic field promotes the refining degree of primary crystallization structure , decreases the chemistry non-homogeneity, So it can strengthen hardness and wearing resistance of weld metal overlay and improve quality of surfacing deposit.This paper talks about plasma arc surfacing Fe-based alloy powder, Ni-based alloy powder alloy powder on low carbon steel with applied intermittent alternative magnetic field. The effect of the intermittent alternative magnetic field on the surfacing deposit solidification structure and mechanical properties is studied and the relationship of different magnetic field types and material wearing resistance has been examined systematically. The mechanism for overlay welding metal during solidification by applied intermittent alternative magnetic field has been discussed intentionally. It shows the shape and distribution of hard phase in overlay welding, and makes theoretical analysis and preliminary discussion. Following are the main results:1、The optimum parameters( the current of magnetic field, the frequency of magnetic field and the duty ratio of magnetic field) of intermittent alternative magnetic field can greatly influence grain structure refinement in plasma overlay.2、The hard phase in weld metal overlay is distributed randomly without magnetic field;With the using intermittent alternative magnetic field, the hard phase in weld metal overlay is fine and distributed "the hexagon" in optimum parameters, then hardness and wear extent in weld metal overlay are higher.3、The result indicated: with the effect of intermittent alternative longitudinal magnetic field, when the optimum magnetic field electric current is 3A, magnetic field frequency is 10Hz and magnetic field duty ratio is 50%, hardness in Fe-based overlay is HRC68, wear loss△G=0.0318g. with the effect of intermittent alternative longitudinal magnetic field, when the optimum magnetic field electric current is 3A, magnetic field frequency is 10Hz and magnetic field duty ratio is 50%, hardness in Ni-based overlay is HRC52.4, wear loss△G=0.39g; with the effect of intermittent alternative transverse magnetic field, when the optimum magnetic field current is 3A, magnetic field frequency is10Hz and magnetic field duty ratio is 50%, hardness of Fe-based overlay is HRC67.7, wear loss△G=0.0323g. with the effect of intermittent alternative transverse magnetic field, when the optimum magnetic field current is 3A, magnetic field frequency is10Hz and magnetic field duty ratio is 50%, hardness of Ni-based overlay is HRC51.7, wear loss△G=0.42g.