A structure of an aquarium heater with off-water overheat protection, wherein a control box with a control circuit is set inside. The control circuit includes: setting a temperature-control module； connecting with an electric heater； and connecting with either an overheat sensor or an off-water protection sensor； wherein the control circuit consists of a single chip, an electric relay box, and a plurality of resistors, capacitors, diodes, and transistors to constitute a complete electric circuit. Therefore, saving the electric energy and avoiding the conditions which the heating temperature is too high or the electric heater is emptily burned to damage because of the off-water can be achieved through the overheat sensor senses the temperature or the off-water protection sensor senses weather the electric heater is off water or not, and then the temperature-control module does the temperature comparison to control the electric heater to heat or not.一種離水過熱保護水族加溫器構造，設有一內具控制電路之控制盒，其中該控制電路包含一溫控模組及連接一電熱器，以及連接一過溫傳感器或一離水保護傳感器其中之一者，該控制電路由一單晶片、一繼電器電匣與多數個電阻、電容、二極體、電晶體構成一完整電路；藉此透過該過溫傳感器之溫度感知及離水保護傳感器感知是否離水，由溫控模組進行溫度比對用以控制電熱器加熱與否，達到節省電能及避免加熱溫度過高、離開水面空燒之情形。
