The possibility of Cu-Al-Ni intermetallic coating on the mild steel through the combustion synthesis has been investigated. In particular, the effect of the ball milling energy on the microstructure of the coating layer was examined to obtain the best coating condition. Experimental results show that Cu-Al-Ni powder compact was explosively synthesized and successfully coated with the steel matrix. It was revealed that the formation of $Cu_9Al_4$ intermetallic decreased with increase in the ball milling energy. This result supports that the high energy ball milling would be effective for obtaining the most suitable microstructure for Cu-Al-Ni coating layer. However, the excessive ball milling energy seems to decrease the bonding strength between the coating layer and the matrix.