The invention discloses a double heading safety electric water heater. The double heading safety electric water heater comprises a preheating heater body, an instant heating device, a high-power safe power source and a connecting electric wire. The preheating heater body comprises a water inlet, a cold water inlet pipe, a pressure release valve, a water inlet control valve, a water outlet, a warm water outlet pipe, a warm water switching valve, a water passing hole, a water insulation switching valve and a temperature displayer, and further comprises a warm water temperature limited switch and a cold and hot water partitioning and adjusting device which is composed of a rotary shaft, an adjusting nut, a fastening nut, a waterproof rubber gasket, a fixed water partition plate, a movable wiper plate, a spring piston, an adjusting shaft and an adjusting flower basket. The high-power safe power source is used for supplying power and is isolated from a 220V power source, so that electric shock accidents are eradicated. Meanwhile, the cold and hot water partitioning and adjusting device is arranged in the preheating heater body, 95% of heated warm water flows into the instant heating device for heating, water scale is avoided, a liner and a magnesium rod are not need, and the double heading safety electric water heater has the advantages of being capable of saving energy, safe, low in cost, large in hot water outlet amount, high in hot water outlet efficiency, facilitating part convenient and the like.