Single layer surfacing test was carried out with high speed electro-slag welding material under the gradient current of 1 200 A, 1 500 A and 1 800 A, the effect of current on chemical composition and FN of surfacing layer was studied, and the microstructure of surfacing layer was analyzed.The single layer electro-slag surfacing material has good weldability under different currents and automatic deslagging after welding, surfacing layer has good flatness and straightness. The results show that the chemical composition,ferrite, hardness, side bending, intergranular corrosion and hydrogen-induced disbonding under different currents meet the requirements of technical conditions. Under the condition of the same surfacing thickness, with the increase of current and speed, the penetration and dilution rate increase, the contents of Cr and Ni of the surfacing layer decreases, and the ferrite content reduces. In engineering application, the ferrite content of the surfacing layer can be controlled by adjusting the welding parameters. The metallographic analysis results show that the microstructure of surfacing layer is austenite +little δ ferrite, after heat treatment, a C migration band about 10 ～20 μm width appears on the fusion line, which is mainly caused by the large carbon content difference between the surfacing layer of ultra-low carbon stainless steel and the medium carbon base metal.