Abstract: To address the problems of low microhardness and poor cavitation resistance of 304 stainless steel, a method of preparing CoCrFeNi high-entropy alloy coatings by laser cladding technology was proposed. The coatings were subsequently annealed at 500 °C for two hours. The microstructure, hardness, and residual stress of the coatings and their effects on cavitation resistance were studied, and the forming mechanism and cavitation damage behavior of high-entropy alloy coatings were revealed. Results indicate that the high-entropy alloy coating by laser cladding is a face-centered cubic (FCC) single-phase solid solution structure, and the overall quality of the coating is excellent, with no obvious pores and cracks. The top region is mainly equiaxed cellular crystals; the bottom is columnar dendritic crystals; the average microhardness is 247.1 HV0.3, which is about 1.4 times that of 304 stainless steel. The coating has good thermal stability. After annealing, the physical phase of the coating does not change, but the dendritic crystal microstructures undergo a slight growth, resulting in a slight softening of the coating. The residual tensile stress on the coating surface is released. The residual stresses σ_x and σ_y in the x and y directions, compared with those of the original coatings, are reduced by 67% and 76%, respectively. Cavitation-induced cumulative mass losses of 304 stainless steel and the coatings before and after annealing are about 13.86、6.38 and 5.94 mg, respectively. The cavitation resistance of the coating is significantly higher than that of stainless steel, with a cavitation rate of 44% to that of the substrate. The CoCrFeNi high-entropy alloy coating can significantly improve the cavitation resistance of 304 stainless steel, and the cavitation resistance is further improved because the residual tensile stress is released after the coating is annealed, resulting in the suppression of cavitation fatigue crack extension.