The utility model discloses a water level sensor, which belongs to the technical field of liquid level sensors and is mainly used for solving the problems of scaling and rusting of a sensor electrode caused by electrolysis and electroplating problems existing in the conventional sensor. The water level sensor is mainly characterized by comprising an O-shaped sealing ring, a plug screw and a mandrel, wherein an injection-molded body formed through injection molding is arranged between the plug screw and the mandrel; the end art of the mandrel is provided with a contact made of an anti-oxidation corrosion-resistant material such as a TC6 material; the end part of the mandrel is provided with a circular hole; the contact is in interference fit with the mandrel; and a colloid is arranged at a contact position between the plug screw and the contact. The water level sensor has the characteristics of accurate alarming, high reliability, long service life and freeness from maintaining, and is mainly used for measuring the liquid level of an anti-freezing fluid in an auxiliary water tank of an automobile.