_{: The coupling field of electrodepositing process under the supercritical fluid was simulated by COMSOL Multiphysics software to study the distribution of the current density and the growth of the electrodepositing coating which was verified by the experimental supercritical composite electrodepositing coating. Simultaneously the surface morphology and microhardness of the experimental supercritical nickel-diamond electrodepositing coating were studied and discussed. The results show that the current density on cathodic edge is much higher than that of the middle section and the predicted growth of the electrodepositing coating accords with current density distribution. The error between predicted and experimental thickness of the central supercritical electrodepositing coating is smaller. The biggest microhardness of the composite supercritical electrodepositing coating can reach 951.47HV(200g), a figure that is 80% higher than that of ordinary composite electrodepositing coating. The supercritical composite electrodepositing coating has smooth surface and compact structure.}