The influence of emulsified oil, suspended solids, Fe³⁺, Fe²⁺, cationic water clarifier and sulfate-reducing (SR) bacteria on the aggregation behavior of residual hydrophobic modified polyacrylamide in treated oily wastewater from polymer flooding was studied by fluorescence spectroscopy and dynamic light scattering. The result of I₁/I₃ showed that the polarity of hydrophobic microdomains increased, whereas the size of the hydrophobic microdomains may be decreased, where the value of I₁/I₃ represents the ratio of the intensity of peak I₁ (374.0 nm) to that of peak I₃ (385.0 nm) of the vibration fine structure of pyrene monomer emission in residual polymer solution. The results of the ratio of I₁ at 48 h to I₁ at 0 h (I_1,48h/I_1,0h) indicated that oil and cationic water clarifier could inhibit the aggregation to some extent, while Fe₂₊ and suspended solids were helpful for aggregation, and Fe₃₊ and SR bacteria had no significant influence on the aggregation of polymer.