In order to improve the dyeing and fixing properties of natural dye on cotton fibers, the mixture of polymaleic acid (PMA) and citric acid (CA) was used for crosslinking dyeing on cotton with natural dye lawsone. The structure of cotton fabrics before and after dyeing was analyzed by FTIR、SEM and XRD, the effect of ester crosslinking on the properties of cotton fabrics and the crosslinking dyeing mechanism with polycarboxylic acid were discussed. The results showed that the surface of the cotton fabric before and after dyeing was not much different, and there was no adhesion between the fibers;The surface of the direct dyeing cotton fiber did not change significantly, and only a small amount of the dyes were attached, more dyes were attached to the surface of the crosslinking dyeing cotton fibers resulting in increased roughness, and the esterification reaction mainly occurred in the amorphous region of the fiber after crosslinking dyeing. Compared with those of direct dyeing cotton fabrics, the dyeing depth(K/S) and the dyeing rate of the crosslinking dyeing cotton fabrics were increased by 88% and 38% respectively, the green light, yellow light and color saturation of the dyed product increased. The colour fastness to rubbing increased by about 1~2 levels, the colour fastness to washing increased by about 1~2 levels. The wrinkle recovery angle (WRA) was enhanced by about 60% and had a UPF value of 50+ after crosslinking dyeing, and it had excellent UV resistance.