A polyamide-imine/polyimide/epoxy resin polymer coating is prepared on the surface of 20CrMo steel by liquid spraying technology which is used to replace the CuPb24Sn copper alloy in valve plates for pumps. Tribological and anti-cavitation erosive experiments of the polymer coating, 20CrMo steel and CuPb24Sn copper alloy are carried out under oil, oil + seawater + silt mixed environment and seawater + silt environment. The results demonstrate that the deposition coating on 20CrMo steel can effectively replace copper alloy for the valve plate of the pump under oil lubrication, oil + seawater + silt environment. Under oil lubrication, the coating exhibits adhesive wear and its average frictional coefficient is 36.63 % and 8.57 % lower than that of the steel and copper alloy, respectively. Likewise, the coating mainly exhibits abrasive wear under the complex working conditions of seawater + silt + oil and seawater + silt. The soft coating reduces the three-body wear and the three-body frictional loss due to the embeddability. Under the complex conditions of seawater + silt + oil, the cavitation mass loss of the coating is 20 % and 35.48 % lower than that of the steel substrate and copper alloy, respectively. In addition, the cavitation mass loss of the coating is 53.6 % and 62.09 % lower than that of the steel and copper alloy under the condition of seawater + silt, respectively. The main influencing factors of the aforementioned results are the lipophilicity of the coating, the large ratio of hardness to elastic modulus (H/E) and the good corrosion resistance.