A high-power plastic aquarium heater includes a narrow, elongated, flat nickel-chrome steel strip wound on a mica tube and electrically connected with a circuit board inside a tubular plastic casing, and vacuum mounts fastened to the tubular plastic casing with pipe clamps for securing the tubular plastic casing to the inside wall of an aquarium. The use of the narrow, elongated, flat nickel-chrome steel strip facilitates positioning of the mica tube in the longitudinal center axis of the tubular plastic casing for even distribution of heat energy. Further, the nickel-chrome steel strip has a broad heat generating surface area in one particular direction to that the high-power plastic heater has a high performance while saving much the consumption of electric power.