Disclosed is a liquid level valve, comprising a valve body, an active valve element, a passive valve element, a positioning magnet, a float mechanism, and a hydraulic mechanism. The float mechanism is disposed on an upper portion of the valve body, and the hydraulic mechanism is disposed at the bottom of the valve body. The float mechanism is used to drive the active valve element in response to a lower limit liquid level, and in turn drive the passive valve element to open a controlled port, thereby switching a switch apparatus to state B. The hydraulic mechanism is used to drive the active valve element in response to an upper limit liquid level, and in turn drive the passive valve element to close the controlled port, thereby switching the switch apparatus to state A.