The invention provides a solar electric heating water tank. A positive temperature coefficient (PTC) heater is arranged in a water tank body with a built-in electric heating tube, the electric heating tube and the PTC heater are connected with a single-chip microcomputer controller outside the water tank body through conducting circuits, and the single-chip microcomputer controller is further provided with a conducting circuit capable of being connected with a solar cell panel. During use, the electric heating tube and the PTC heater can be switched automatically through the single-chip microcomputer to heat water in the water tank body. When sunshine is insufficient, and the voltage is low, the PTC heater is started to heat the water through low power, when the sunshine is sufficient, the electric heating tube is started to heat the water through high power, and solar energy resource can be fully used.