The cationic dye is a special dye for acrylonitrile fiber. The dyeing method is in a weakly acidic (pH 4.5 or so) bathtub with acetic acid and sodium acetate as a buffering agent, and close to boiling dyeing in the presence of a dielectric and an appropriate amount of auxiliary agent. The dyeing mechanism can be divided into three steps: 
(1) The dye cations in the dyebath are adsorbed on the surface of the fiber.
(2) The dye cation diffuses from the surface of the fiber to the inside.
(3) The dye cation is salt-bonded to the anionic group contained in the fiber.
Under normal dyeing conditions, the salt formation in the last step is an irreversible reaction, which results in high fastness and uneven dyeing. The first two steps are fast, and the second step is slow. It determines the overall dyeing speed. Since the affinity between the dye and the fiber is large, in order to obtain the leveling effect, the dye bath temperature, pH value, electrolyte, retarding agent, etc. must be strictly controlled.