This solution adopts a molecular sieve adsorption and low-pressure process technology of turboexpander refrigeration. After removing the mechanical impurities such as dust in the air filter, the raw air enters the air turbine compressor, then enters the air cooling tower to exchange heat with water, and then enters the molecular sieve adsorber. Part of the gas is drawn from the middle of the main heat exchanger, enters the expander, and the expanded air enters the upper tower. After the air enters the main heat exchanger, it is cooled to the saturation temperature by the return gas and enters the lower tower with a small amount of liquid. After the air is initially rectified by the lower tower, an oxygen-enriched liquid air is obtained in the lower tower. After the liquid air is cooled by the cooler, it is throttled into the upper tower. After the upper tower is further rectified, oxygen with a purity of 99.6% is obtained at the bottom of the upper tower. The oxygen of this product is reheated by the main heat exchanger and then sent out to the user after being discharged from the cold box. 99.999% nitrogen is obtained from the top of the upper tower, and it is returned to the cold box after being reheated by the cooler and the main heat exchanger. The polluted nitrogen is led out from the top of the upper tower, reheated by the cooler and the main heat exchanger, and then exits the cold box. After being heated by the regeneration heater, it is used as the molecular sieve regeneration gas and the excess gas is vented. The argon fraction extracted from the upper and lower part of the upper column enters the bottom of the crude argon column 1, and the rising steam is extracted from the top of the crude argon column 1 into the bottom of the crude argon column 2. After rectification of the two columns, the Crude argon, most of the crude argon enters the condenser of the crude argon column, is condensed into liquid by the liquid space, and is refluxed to the crude argon column as the reflux liquid of the crude argon column. The liquid returned to the crude argon column 2 is sent to the top of the crude argon column 1 after being pressurized by a liquid argon pump. After the crude argon column 1 is rectified, the liquid fraction returns to the upper column from the bottom, and part of the crude argon enters the argon argon column. After the rectification of the argon column, the required pure argon can be obtained at the bottom of the argon column.