Potential of hydrolyzed polyacrylamide (HPAM) biodegradation to final products was studied through regulating its own nitrogen transformation. Under the conditions of 2, 3 and 4 mg/L of DO, HPAM removal ratio reached 16.92%, 24.51% and 30.78% and the corresponding removal ratio reached 49.15%, 60.25% and 76.44% after anaerobic biodegradation. NO3--N concentration was 9.43, 14.10 and 17.99 mg/L in aerobic stages and the corresponding concentration was 0.17, 0.07 and 0.008 mg/L after anaerobic biodegradation. Oxygen as electron acceptors stimulated the activities of nitrification bacteria and other functional bacteria, thus further enhanced nitrification and HPAM biodegradation. NO3- (from HPAM oxidation) as electron acceptors stimulated the activities of nitrate-reducing, acetate-producing and methanogenic microorganisms and they could form a synergistic effect on denitrification and methanogenesis. Thermodynamic opportunity window revealed that NOx- could accelerate anaerobic HPAM bioconversion to methane. Aerobic and anaerobic growth-process equations of cells verified that the metabolism on HPAM was feasible.