Abstract: The aluminum-bronze power and copper power were overlaid on the low carbon steel by plasma arc.After the contrast experiment in different surfacing processing parameters,the influence of the penetrating crack and gas porosity were analyzed.The experiment results show that the tendentiousness and probability of the penetrating crack and gas porosity increase obviously with the energy input increasing.The generation of the penetrating crack was affected by stress state,stress intensity,chemical constitution of the surfacing power and original condition of base metal.The low-melting eutectic and the microcrack were the main causes,the wetting spreadability of the liquid aluminum-bronze and the tension stress were inducement.As long as the surfacing processing procedure and measures were appropriately tocken the penetrating crack and gas porosity could be avoided or reduced.