The invention discloses a water retaining cover structure and a water heater. The water retaining cover structure comprises a box-shaped body, a gap is formed in the bottom face of the box-shaped in the length direction, and a penetrating hole allowing a water inlet pipe to penetrate through is formed in the side wall of one end of the box-shaped body. According to the water retaining cover structure, the box-shaped body structure with the bottom provided with the gap is arranged, when water is discharged from a water inlet pipe inserted into the box-shaped body, the water flow impacts the inner wall of the box-shaped body, after pulling back, the water flow flows out of a water retaining cover from the gap formed in the bottom of the box-shaped body, compared with an existing water retaining plate, the water flow impact is much more gentle than the previous water flow impact, the water flow obtained after structure optimization upwards pushes a hot water layer to be more gentle, the water temperature layering disturbance of an inner container of the water heater can be greatly reduced, the hot water use rate is higher, and the hot water output rate is improved.