The liquid nitrogen generator (liquid nitrogen machine) is composed of three parts: nitrogen generator (built-in or external), refrigeration equipment (gas liquefaction equipment) and Dewar tank. The whole machine has the function of automatic liquid replenishment with one key, and the equipment starts automatically when the liquid nitrogen in the liquid nitrogen tank is lower than the set liquid level. Liquid nitrogen machine manufacturing adopts the principle of mixed mass throttling refrigeration, cooling nitrogen from the ambient temperature to the saturation condensing temperature of nitrogen liquefaction step by step, the lowest temperature of refrigeration machine refrigeration can be up to -196 °, the liquid nitrogen liquefied in the refrigeration evaporator is transported to the liquid nitrogen tank to save the liquid nitrogen to obtain liquid nitrogen, the equipment automatically detects the liquid nitrogen level in the Dewar tank, and fully automatic control of the operation of the equipment.