Abstract: Cationic flocculant of quaternary ammonium salt of lignin was synthesized using sulphate lignin from papermaking black liquor.The decolourizing performance of quaternary ammonium salt of lignin and effects of different catalysts on the synthesis were studied.Quaternary ammonium salt of lignin was investigated through infrared spectrum(FTIR).Flocculation performance of the salt applied to dye liquor of high concentration and high colority has been quantitatively analysed. Results indicate that cationic flocculant of quaternary ammonium salt of lignin can be synthesized by grafting reaction.Synthesis of monomeric quaternary ammonium salt was carried out at:mole ratio of tri methylamine and chloro cyclopropane 1:0.7, temperature from -3℃ to -6℃.Ammonium supersulphate is a favorable catalyst by contrasting different catalysts at dosage 0.5%. Quaternary ammonium salt of lignin was used as flocculant for decolorizing dye waste water at 2-3 g/L in acidic condition(pH value 2-3).This modified natural macromolecule product is a flocculant for dye wastewater with favorable performance.