The invention relates to a water-cooled line engine body, which belongs to the technical field of power devices. The water-cooled line engine body comprises cylinder holes, crankshaft boxes, cooling water cavities, partition boards, partition board cooling water channels, partition board cylinder cover bolt holes, centre cylinder cover bolt holes of cylinders, engine body and main bearing cover combination surfaces, main bearing bolt holes, an engine body admission side, an engine body exhaust side, a cooling water inlet, a main oil duct on the engine body admission side and the main oil ducton the engine body exhaust side. The water-cooled line engine body is characterized in that: the engine body admission side and the engine body exhaust side are both provided with longitudinally-arranged reinforcing ribs and transversely-arranged reinforcing ribs; the peripheral directions of the cylinder holes are provided with inclined reinforcing ribs and vertical reinforcing ribs; great transitional circular arcs are arranged between the inclined reinforcing ribs and the vertical reinforcing ribs; and the engine body cooling water inlet is provided with water inlet reinforcing ribs. The water-cooled line engine body can enhance rigidity and strength in a vertical direction to a great extent, reduce the vibration amplitude of the engine cylinder in the vertical direction and prolong the service life of an engine.