The invention discloses an independent heating-external plastic liner water heater. A liner and a heating liner are arranged in an outer shell; the liner adopts a plastic cylindrical structure; reinforcing ribs are regularly distributed on the outer wall of the liner; an iron sheet reinforcing layer is wrapped on the outer side of the liner; an electric heating pipe and a temperature control adjuster are arranged in the heating liner; a water inlet and outlet system comprises a water outlet pipe and a water inlet pipe; the liner and the heating liner are connected through the water inlet pipeand the water outlet pipe; a water inlet tee joint is formed in the middle section position of the water inlet pipe, and is connected with an upper water pipe in the external; a water outlet tee jointis formed in the middle section of the water outlet pipe, and is connected with a water outlet of the outer shell of the water heater; a control panel is arranged on the surface of the outer shell; and the control panel is connected with the temperature control adjuster through a circuit. The independent heating-external plastic liner water heater changes the material of the liner, uses the reinforcing ribs and the iron sheet reinforcing layer for preventing the water leakage, and effectively prevents multiple dangerous conditions through external positioning of the heating liner.