The invention relates to the field of textile printing and dyeing, and discloses a method for improving the dye-uptake of direct dyes on cotton fabrics. The method comprises the following steps that (1) the cotton fabrics are treated by a chitosan solution, specifically, the pretreated cotton fabrics are completely immersed in the chitosan solution, then an excess solution is rolled out, pre-roasting is conducted, heating and solidifying are conducted, then washing is conducted in a weakly acidic solution, and then drying is conducted; and (2) dyeing is conducted, specifically, the treated cotton fabrics obtained in step (1) are placed in a direction dye solution for stirring, then heating and heat preservation are conducted, and the cotton fabrics are soaped and dried; wherein in the step(1), the preparation method of the chitosan solution comprises the steps that chitosan is dissolved in a citric acid solution with the concentration of 40-50 g/L; and the concentration of the chitosan solution is 10-15 g/L. According to the method, citric acid is used as a crosslinking agent, the chitosan is crosslinked on the cotton fabrics, and the dye-uptake of the direct dyes on the cotton fabrics is improved.