The invention discloses an electric heater which comprises an electric heating pipe and a sleeve; the electric heating pipe comprises a quartz pipe and an end seal; an electric heating film is attached to the inner wall of the quartz pipe; the end seal is connected to the end of the quartz pipe in a sleeving mode; the sleeve is provided with a water inlet, a heating cavity, a detection cavity anda water outlet which communicate sequentially; the sleeve is provided with a mounting opening communicating with the heating cavity; the quartz pipe extends into the heating cavity and the end seal tobe fixed to the heating cavity in an airtight mode through the mounting opening; a water inlet valve is arranged at the water inlet; the sleeve is provided with an electrically controlled assembly extending into the detection cavity; and the water inlet valve and the electric heating pipe are electrically connected with the electrically controlled assembly. According to the electric heater, through the mode that a fluid passes through the heating cavity to be circularly heated around the electric heating pipe, heating is even, the heat exchange efficiency is effectively improved, and the danger caused by explosion of the electric heating pipe is effectively prevented.