The invention discloses a high-cavitation-resistance composite coating. The composite coating consists of amorphous substances, nano-crystalline substances and borides, wherein the composition in percentage by weight of elements is: more than or equal to 6 percent of B, 3 to 6 percent of Si, 20 to 55 percent of Cr, 10 to 20 percent of Ni, 2 to 4 percent of Mo, and the balance of Fe; the thicknessof the composite coating is 100 to 400 mu m; and the amorphous substances and the nano-crystalline substances in the composite coating account for 40 to 80 percent of the volume of the composite coating. A preparation method comprises: directly spraying and depositing alloy powder melted by high-speed flame onto a substrate material; simultaneously supplying cooling gas to a deposition surface and/or placing a workpiece needing deposition on a copper-base pedestal; and synchronously preparing the composite coating containing not only the amorphous substances and the nano-crystalline substances but also the borides. The composite coating has high hardness and high wear resistance, and in particular, the formation of the nano-crystalline substances needs no subsequent annealing treatment.