The liquefaction unit of small liquid nitrogen air separation plant is divided into low pressure liquefaction cycle and medium pressure liquefaction cycle. The circulating medium can be air or nitrogen. Small liquid nitrogen air separation plant can produce a certain amount of liquid oxygen and liquid nitrogen or all liquid nitrogen at the same time according to the needs. The liquefaction uint of small liquid nitrogen air separation plant can adjust the amount of liquid oxygen and liquid nitrogen according to the amount of oxygen and nitrogen emission. Therefore, it can be used as an auxiliary equipment to regulate the air separation load and reduce the oxygen emission in the oxygen plant. If large liquid storage tank and liquid evaporation system are equipped, the peak regulating system of oxygen and nitrogen pipe network can be formed. When the pipe network pressure is low, taking liquid oxygen and liquid nitrogen out from the liquid tank, convert them into oxygen and nitrogen by pr
