The ceramic coating technology of microarc oxidation (MAO) was utilized to modify surface properties of the movable endplate of a high pressure gear pump used in water-hydraulic system, which is made of aluminium alloy. A coMPact ceramic layer of more than 130 μm was developed on the movable endplate with the hardness up to HV1000 by means of microarc oxidation. A trial of tests conducted in a water power transmission system show that the maximum outlet pressure of the gear pump with the movable endplate treated by microarc oxidation, can reach 16 MPa. It is pointed out that the ceramic coating developed by microarc oxidation tech nology on the surface of aluminium alloy, is economical and feasible.