Plasma spray welding is a very important and rapidly developing method in surface modification technology. It can strengthen the surface properties without changing the matrix materials, such as improving the wear resistance, corrosion resistance, high temperature oxidation resistance and service life of materials. At the same time, as a new coating material, high entropy alloys (HEAs) has different performance characteristics from traditional coating materials because of its four effects:high entropy effect in thermodynamics, hysteresis diffusion effect in dynamics, lattice distortion effect in structure and cocktail effect in performance. The alloy can have high hardness, high wear resistance, high corrosion resistance and high interfacial compatibility at the same time. At the same time, the alloy elements can be optimized by phase composition prediction and phase diagram simulation, which has good research value. In this paper, FeCoCrNiMo high entropy alloy powder was used as coating material, and high entropy alloy plasma spray welding layer was prepared by plasma spray welding technology. The effects of different Mo content on the microstructure and corrosion resistance of the welding layer were studied.