The invention provides a method for producing citric acid, which comprises the step of inoculating Aspergillus niger to a fermentation medium so as to carry out fermentation in fermentation equipment under the conditions of generating citric acid and introducing air. The method for producing citric acid is characterized by also comprising the step of introducing CO2 gas into the fermentation equipment. The citric acid produced by the method provided by the invention has higher fermentation acidity, higher conversion rate of the citric acid and lower fermentation residual sugar; and the invention has the advantages of simple process and easiness in operation.