Under normal working conditions, the oxygen concentration of the oxygen generator is stable when outputting oxygen at the rated flow rate. When outputting oxygen exceeding the rated flow rate, the oxygen concentration decreases. The reason is easy to understand as it exceeds the oxygen production capacity. However, there is another phenomenon that when the oxygen generator operates at a very low flow rate below the rated flow rate, the oxygen concentration will also decrease. This is difficult to explain by oxygen production capacity. At present, there is no scientific explanation and conclusion for the phenomenon of reduced oxygen concentration when operating at low flow rates. Personally, it is understood that low flow output leads to an increase in the gas remaining in the molecular sieve container within the rated period. The excess gas saturates the adsorption capacity of the molecular sieve, and part of the nitrogen overflows, resulting in a decrease in oxygen concentration. Therefore, in order to ensure that the oxygen concentration is not troubled by changes in flow rate, the upper flow limit restriction and lower flow compensation of this product will solve this problem.