To improving the cavitation erosion resistance (Re) of the FeCoCrNiB0.2 high entropy alloy (HEA), the FeCoCrNiB0.2 + WC (0 wt.%, 20 wt.%) HEA coatings were synthesized with premixed high-purity on Q235 steel by laser cladding (LC). The effects of WC on the hardness and Re were investigated. The cavitation erosion (CE) behavior in distilled water and 3.5 wt.% NaCl solution and microhardness were evaluated using an ultrasonic vibrator and Microscopy/Vickers hardness tester. The cavitation mass loss and surface morphology were used to characterize the cavitation damage. Experimental results showed that the Vickers hardness of FeCoCrNiB0.2 + 20 wt.% WC coating was higher than that of FeCoCrNiB0.2 coating, and the cumulative mass loss of FeCoCrNiB0.2 + 20 w.t% WC coating was less than that of FeCoCrNiB0.2 coating. The presence of chloride ion interacts with CE, forming a combined cavitation-corrosion damage, which accelerates the removal of material from the surface. Adding 20 wt.% WC, the number of cavitation pits was significantly reduced and the depth of pits also became shallower, which means that the addition of WC could weaken the degree of cavitation damage.