The study provides an insight into the oil washing mechanism of hydrophobically associating polyacrylamide (HAHPAM) in chemical flooding from the perspective of extensional rheology. The extensional rheology of HAHPAM solution was systematically investigated under different influencing factors (concentration, temperature, NaCl and surfactant) using capillary breakup extensional rheometry (CaBER). Compared with partially hydrolyzed polyacrylamide (HPAM), the HAHPAM solution shows better extensibility due to the additional hydrophobic interaction between molecular chains, particularly at high temperature and high salinity. By increasing the concentration and decreasing the temperature, the filament breakup time and extensional viscosity of the HAHPAM solution increase. NaCl delays the attenuation of the HAHPAM filament by increasing the solution extensional viscosity and surface tension. In the presence of sodium dodecyl sulfate (SDS), the reduced surface tension dominates the stability of the filament and weakens the extensibility of the HAHPAM/SDS composite solution.