Many spare parts used in various industries like mine, electric power and so on are required to have enough toughness and strength as a whole ,and have high surface hardness and high surface wear resistance. In order to meet the demands above mentioned, composite alloy material reinforced with hard grains has been developed on surface of common steel castings by self designed brazing process. The effects of different granularity proportion and volume fraction of WC grains as wear resistant phase on microstructure and abrasiveness of composite alloy were studied by experiment. The research results were then applied to wear resisting supporting roller and disc pad used in middle speed coal crusher. Experimental research shows that microstructure compactness and wear resistance of composite alloy can be significantly improved when compactness (bulk density) and volume fraction of wear resistant phase in composite alloy increase within limits. In the present paper, composite alloy is provided with better abrasiveness when bulk density of WC grains is 10 32 g/cm 3 and their volume fraction varies between 25%～54%. Besides, wear resistance of composite alloy is up to the best when volume fraction of WC grains is 54%. Applied results prove that composite alloy supporting roller and disc pad prepared by brazing process have advantages of thick(10～30mm)and high quality wear resistant cladding, convenient installation, high property to price ratio, obviously economic effect and good wear resistance ,etc. The wear resistance of composite alloy is 35 times more than that of cast steel and 15 times more than that of high chromium cast iron and that of nickel hard cast iron No.Ⅳ.