In order to remove anionic trash in whitewater effectively to improve the recycling of paper-making whitewater. In this paper, chitosan microsphere was prepared, and modified with glutaraldehyde, then the adsorption of chitosan microsphere and its modifier for poly-galacturonic acid were studied. The results showed that the cross-linking of chitosan microsphere and glutaraldehyde followed the pseudo-second-order equation and Freundlich equation. As the pH of poly-galacturonic acid solution increased, the adsorption quantity of chitosan microsphere and its modifier for poly-galacturonic acid gradually decreased first and then increased, but at the same pH, the adsorption quantity of modified chitosan microsphere for poly-galacturonic acid was larger than that of chitosan microsphere. In addition, with the gradual increase in concentration of sodium chloride, the adsorption quantity of chitosan microsphere and its modifier for poly-galacturonic acid rapidly decreased, but at the same concentration of sodium chloride, the adsorption quantity of modified chitosan microsphere for poly-galacturonic acid was slightly larger than that of chitosan microsphere.