A low-temperature device for separating and purifying gas based on a small-sized low-temperature refrigerating machine includes a primary heat exchanger, a secondary heat exchanger, a quaternary heat exchanger, at least one small-sized low-temperature refrigerating machine, and at least one liquid collecting tank. The small-sized low-temperature refrigerating machine includes a first cold head and a second cold head, the secondary heat exchanger is provided on the first cold head to form a primary cold head heat exchanger, the quaternary heat exchanger is provided on the second cold head to form a secondary cold head heat exchanger, a mixed gas outlet is connected to an inlet of the primary cold head heat exchanger, an outlet of the primary cold head heat exchanger is connected to an inlet of the liquid collecting tank, and a gas outlet of the liquid collecting tank is connected to an inlet of the secondary cold head heat exchanger. By using primary and secondary cold heads of the small-sized low-temperature refrigerating machine as cold sources, gases having different condensing temperature are liquefied and solidified separately, accordingly a high-purity gas having a lower condensing temperature is obtained, and two or more gases can be separated and purified at a lower cost.