The utility model provides an electric heater of liquid, which comprises a metal outer pipe whose middle portion is provided with resistance wires, wherein insulated heat conducting materials are filled between the resistance wires and the metal outer pipe, and a thermostable insulating cannula is coated on the surface of the metal outer pipe. The electric heater of liquid adopts a Teflon cannula or a medlin cannula with high-temperature antisticking property and excellent chemical corrosion prevention property simultaneously as the thermostable insulating cannula. The cannula can effectively prevent a metal electric heating pipe body of an electric heater and heated liquid from directly contacting, avoids a metal electric heating pipe body from etching and fouling, and improves the service span of electric heating elements in the electric heater.