The bio-doubling process was applied to the treatment of pig breeding wastewater to meet the discharge standards stably. The results showed that the effluent concentrations of CODCr and ammonia nitrogen by the bio-doubling process met the Class I discharge standard of Integrated Wastewater Discharge Standard (GB 8978—1996) ( cCODCr ≤100 mg /L、cNH+4-N ≤15 mg /L), when reflux ratio was 50 ∶ 1, HRT was 150 h, DO concentration was 0.3~0.5 mg /L and MLSS concentration was 6~8 g /L. Compared with the traditional A/O process, the bio-doubling process reduced about 30% of the floor area, 70% of hydraulic retention time and 50% of power consumption per ton water for the pig breeding wastewater treatment.