This paper talks about that the DC/AC longitudinal magnetic field has been applied to the plasma arc surfacing welding of Fe-based and Co-based alloy powder on low carbon steel respectively.The influence of electromagnetic effect on the microstructure and properties of surfacing deposit has been investigated with different parameters of magnetic field.The effect of different parameters of the DC/AC longitudinal electromagnetic field on the hardness,wearing resistance and microstructure of two alloys in surfacing layer has been systematically researched by using scanning electronic microscope,wear test and macro hardness testing.The results have indicated that proper magnetic parameters can increase the amount of hardening phase in overlay deposit,control the growth direction of hardening phase and improve the hardness and wear resistance of the surfacing overlay.Moreover,the principle of electromagnetic effect has been analyzed and illustrated in brief.