This study was conducted to investigate the purification capacity of the freshwater mussel Anodonta woodiana on nitrite (NO2－-N) in rearing water. The effect of nitrite on the mussels’ clearance rates was analyzed. Furthermore, the nitrite concentrations, removal efficiencies, and purification efficiencies were compared at the control (0 mussels/m3), low (10 mussels/m3), medium (20 mussels/m3), and high (30 mussels/m3) culture densities and different treatment times (24, 48, 72, and 96 h). The results showed that the clearance rates of A. woodiana in the blank (0 mg/L) and nitrite-treated (1.0 mg/L) groups were 232.1 ± 122.3 L/(h·kg) and 69.0 ± 17.7 L/(h·kg), respectively, they did not reach a significant difference level (P > 0.05). The lowest nitrite concentration in the rearing water was 0.20 ± 0.06 mg/L for A. woodiana at low culture density and 96 h treatment, and the corresponding removal efficiencies and purification efficiencies could reach (64.99 ± 10.32)% and 90.16 ± 13.54 mg/(h·kg), respectively. The effect of A. woodiana on nitrite concentrations and removal efficiencies was significantly correlated with culture density and treatment time (P < 0.05), while the interaction with both was not significant (P > 0.05). The purification efficiencies of nitrite was only significantly correlated with culture density (P < 0.05). These findings showed that A. woodiana could effectively purify the higher levels of nitrite in the rearing water, and the best purification effect was achieved at a culture density of 10 mussels/m3.