The invention discloses a cold water backflow heating device of an instant electric water heater. The device comprises a first pipe body and a movable pipe body, wherein the first pipe body is connected to the movable pipe body in a sleeving manner; one end of the movable pipe body is provided with a movable port and the other end of the movable pipe body is provided with a telescopic hose; the other end of the telescopic hose is provided with a fixed pipe body; one end of the first pipe body is provided with an opening, and the other end of the first pipe body is provided with a first outer ring; the first outer ring is arranged on a water outlet pipe body; and the outer side of the first outer ring is provided with a low-pressure pipe body. According to the invention, the heating deviceof the electric water heater is improved, so that water in the water outlet pipe of the water heater enters a heating pipeline in a state that the valve is closed; and the water heated inside the water heater is used for heat preservation, and hot water is directly discharged after air is discharged when the water heater is opened, so that water resources are effectively saved, cold water is not generated, and the electric water heater is convenient for bathing.