Abstract: A three-mode geomagnetic detector is provided. The detector includes an upper cover, a lower casing, and an inner container. A bottom of the inner container is detachably connected to a bottom of the upper cover, the inner container is sleeved within the upper cover, and the upper cover is snap-fitted to the lower casing. Through the design of the inner container, the use of an O-shaped sealing ring is avoided, such that poor sealing caused by the O-shaped sealing ring deformation due to vehicle rolling is avoided, and opening for replacement of components is convenient.