A liquid level detection system for a liquid nitrogen tank, including a detection device and an alarm display, the detection device includes: a liquid nitrogen tank cover, a switch assembly, a float, a hanging wire, and an information processing and transmission assembly, and the switch assembly and the information processing and transmission assembly are installed on the Inside the liquid nitrogen tank cover, the floating ball is connected with the switch assembly through the hanging wire; the alarm display, including the stabilized power supply, the second radio transceiver module, the second single-chip microcomputer, the liquid crystal display, the buzzer and the RS232‑USB interface converter are all installed It is located inside the chassis, and communicates data with the information processing and transmission components through wireless data transmission technology. The advantage is that the system has a long-distance communication detection function, and can combine the liquid level detection device with the liquid nitrogen tank cover, low power consumption, battery power supply, accurate alarm liquid level, and one alarm display can display multiple liquid nitrogen The level status of the tank.