Abstract: The hydrophobically associating water-soluble acrylamide-modified copolymers（PASA）with butyl styrene（BS）and sodium-2-acrylamido-2-methylpropane sulphonate（NaAMPS）were synthesized by the micellar free radical copolymerization technique.The two key problems including the very poor water-solubility and thermal stability of the hydrophobically associating water-soluble polymers are overcome in this study，which are due to the incorporation of the anionic monomer NaAMPS into the PASA molecules and the phenyl group from BS which can stabilize the hydrophobic units.The influence of reaction conditions on the apparent viscosity of PASA aqueous solution was studied，and the suitable reaction parameters including mole percentage of NaAMPS，mole percentage of BS，mole percentage of initiator，relative to total monomers，mass percentage of total monomers in water，mass percentage of surfactant in water，reaction temperature，pH value and reaction time were 10%，2.5%，0.07%，10%， 6.0%，50℃，pH 6—7 and 12 h，respectively.Under the above reaction conditions，the polymer was synthesized，which critical association mass concentration was about 0.05 g·dl^-1.The apparent viscosities of 0.05 g·dl^-1 and 0.1 g·dl^-1 PASA aqueous solution were 283 mPa·s and 1020 mPa·s，respectively.The synthesized product was characterized with UV，FT-IR，¹H-NMR and elemental analysis.The block-structure of the polymer was shown by DSC measurement，which was favourable to the intermolecular hydrophobic association.