The P(AM-DAC-BA), one kind of hydrophobically associating cationic polyacrylamide(HACPAM), was synthesized with acrylamide (AM), acryloyloxyethyltrimethyl ammonium chloride (DAC) and butylacrylate (BA) by the micellar free radical copolymerization technique. The reaction was carried out under the irradiation of UV light. The effects of main factors, i.e. monomers concentration, mass ratio of AM and DAC、BA ratio、CTAB ratio、photoinitiator concentration and irradiation time on the molecular weight were investigated. The results showed that HACPAM with the molecular weight of 849×10 4 can be synthetized when the monomer concentration was 30%, the mass ratio of AM and DAC was 70:30, the BA ratio was 2%, the CTAB ratio was 2%, the initiator concentration was 3‰ and the irradiation time was 100 min. The chemical structure and performance were characterized by FT-IR, SEM, DTA-TGA. The results showed that the polymerization reaction between monomer happened, the HACPAM was synthesized. In addition, the polymerizate heat stability was fine.