This invention relates to a device for coating shell of water pump, comprising a base and two side baffles, wherein a fixed grillage is set above between the side baffles; a left axle and a right axle are installed on the fixed grillage; both the left axle and the right axle are connected with number one belt wheels that are attached with the belt; the sliding seat with a spray gun mounted on the lower part is hooked by the belt; the left axle is connected with a reciprocating reversible component that is equipped with main driving motor.The left axle is connected with a multiple reversible component which conducts linkage with the front axle by number two belt wheel; there is a supporting bracket arranged right below being a leading screw. The leading screw thread is connected with the mounting holder; the leading screw is linked with number two belt wheels and with the fag end between two belt wheels. This invention can automatically complete the process that sprays glue coating on and inside the complicated grooves to the shell of water pump in simple and convenient controlling way, thereby accelerating the efficiency and quality of glue auto-spraying.