Liquid level sensor and liquid level sensing system

The embodiment of the invention provides a liquid level sensor and a liquid level sensing system, so as to generate an optical feedback signal which changes along with the change of differential pressure between a high-pressure side and a low-pressure side of a liquid level container to be detected. Thus, the optical feedback signal is processed to measure the liquid level of the liquid level container to be detected. The liquid level sensor comprises a fluid cavity, a diaphragm, an FBG cavity which is arranged at the part, located in the fluid cavity, of the optical fiber, the optical fiber which is used for transmitting an optical signal to the fiber bragg grating sensor through the FBG cavity and receiving an optical feedback signal generated by the fiber bragg grating sensor through the FBG cavity, a fiber bragg grating sensor which is used for sensing the strain of the diaphragm and generating an optical feedback signal changing along with the change of differential pressure between the high-pressure sid