The bio-doubling process was applied to the treatment of pig breeding wastewater to meet thedischarge standards stably. The results showed that the effluent concentrations of CODCr and ammonianitrogen by the bio-doubling process met the Class I discharge standard of Integrated Wastewater Dis-charge Standard ( GB 8978—1996) ( cCODCr ≤100 mg /L、cNH+4-N ≤15 mg /L) ,when reflux ratio was50 ∶ 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 floorarea,70% of hydraulic retention time and 50% of power consumption per ton water for the pig breedingwastewater treatment.