Abstract: A hydrophobically associating cationic polymer P (DMC-HDMC) has been synthesized in aqueous solution by radical copolymerization, of which has been characterized in terms of infrared spectrum and fluorescence spectrum. Its acid solution properties have also been studied compared with polymer PDMC. Results have shown that, the structure of P (DMC-HDMC) was in consistent with what we have expected bearing long methane chain (CH2) 16; hydrophobic domain formed in aqueous solution and the critical associating concentration(CAC) of P (DMC-HDMC) was about 1700ppm; in 20wt% HCl solution, when the concentration of P (DMC-HDMC) were 0.16wt% (CAC）, their corresponding outlet time were 20.47s and 40.8s respectively; apparent viscosity of PDMC in acid solution gradually decreased with increase of acid concentration, while P (DMC-HDMC) changed little and even slightly increased as a whole.