The invention relates to the technical field of diesel engines, in particular to a urea pump for treating tail gas of a diesel engine. The urea pump mainly comprises a motor, an eccentric wheel, a connecting rod, a bearing, a membrane, a pump body, a valve seat, a valve deck, valve plates, a rear cover, a rear cover bearing and a set screw, wherein an output shaft of the motor is fixedly connected with the eccentric wheel, an excircle of the eccentric wheel is connected with an inner ring of the bearing, an excircle of the bearing is connected with the connecting rod, and the connecting rod is fixedly connected with the membrane, so that a reciprocating mechanism is formed; the front end of the motor is fixedly connected with the pump body, the bearing is arranged at the rear end of the pump body, and the rear cover of the pump is fixed on the pump body; screw holes for fixing the membrane and a pump cover are formed in the upper end of the pump body; and the valve seat provided with an arc pump cavity is assembled on the membrane, and a rectangular valve block used for controlling water to flow in and out is arranged in the valve seat. The urea pump has the advantages of simple structure, small size, low cost, flexibility in flow control, convenience in use and the like, and doesn't require to be lubricated during operation.