The invention discloses a visual chromatic aberration method for judging the dissolution degree of cation polyacrylamide in water, relating to a method for effectively using a polymeric flocculant during flocculation separation of zymotic fluid or sewage. The visual chromatic aberration method can effectively prevent the incompletely dissolved cation polyacrylamide from entering into a flocculation system and influencing flocculation effect. In the visual chromatic aberration method, a water-soluble colored matter is dissolved in a cation polyacrylamide-water system; when the system contains the incompletely dissolved cation polyacrylamide coagulum, the water-soluble colored matter can not enter into the inside of the coagulum rapidly, which causes the color of the coagulum to be lighter and the color of water solution around the coagulum to be deeper, thus a large chromatic aberration is formed, and the size of a color spot is easy to identify visually. The smaller the size of the color spot, the larger the dissolution degree of the cation polyacrylamide, and vice versa. By using the method, operating conditions for completely dissolving the cation polyacrylamide with different specifications in the water can be easily mastered, therefore, the flocculation separation efficiency of the zymotic fluid or the waste water is improved, and the quality and the quantity of paper in papermaking can be improved.