The invention discloses a water cooling exhaust pipe of a multi-cylinder diesel engine. A right side plate, a top plate, a baseplate, a back plate, a front plate and a left side plate are combined andwelded to form a cylinder; a water inlet pipe is welded in a mounting hole on the baseplate; a water outlet pipe is welded in a mounting hole on the top plate; the cylinder is welded on the left endsurface of the left side plate; a silencer connecting flange is welded on the left side surface of the cylinder; an exhaust main pipe is welded in a center hole of the silencer connecting flange; an exhaust branch pipe is welded in the radial direction of the exhaust main pipe; and an engine exhaust port connecting flange is welded on the front side surface of the exhaust main pipe. Through use ofa water cooling exhaust system, the temperature of a diesel generator set in the operating process is obviously lowered, the unit output power is greatly improved, and meanwhile, an obvious effect onthe unit noise reduction is achieved.