The utility model discloses an alarm device for an excessively low water level, and relates to the field of manufacturing technologies of heavy truck engines. The alarm device comprises a floater, magnetic steel and a reed pipe. The alarm device is provided with a base which is provided with a guide sleeve. A guide rod which stretches out of the guide sleeve is inserted into the guide sleeve of the base, the floater is installed at the top of the guide rod, and the magnetic steel is arranged at the bottom of the guide rod. The reed pipe is arranged close to the bottom of the guide sleeve of the base. Compared with the prior art, the problem that because an existing alarm device for the excessively low water level attracts iron scraps or other metal impurities, an alarm fails can be solved.