As the diamond surface has higher interface energy, the adhesion of surface and matrix is bad, and it makes the diamond shatter easily. For solving this, the microstructures and properties of the metallic coating on the diamond surface which contains W (tungsten) by hydrothermal method are studied. The different temperatures such as 110 ~140°C and 5h insulating were adopted to be coated in high pressure reactor respectively. The metallic coating on the diamond surface was studied by SEM，XRD and so on. The results show that the continuous and compact coating of Ni and W on the diamond surface is formed by the hydrothermal coating technology at 130°C. The heat treatment temperatures were maintained at 850°C for 1h during the heat treatment process. After the corresponding heat treatment, the better layer coatings, of which thickness is about 10μm, are formed for protecting diamonds and reducing the trend of oxidization. The carbide WC (tungsten carbide) at the interface between the coating and diamond surface is formed. The chemical and metallurgical bonding between diamond and coating is obtained. Because of the coating layers formed and the defects on diamond surface made up, the compress strength of diamond after hydrothermal and heat treatment is enhanced. The compressive strength after hydrothermal and heat treatment is higher than that of un-coating particles(those are 29.45% and 83.64% respectively).