When digested piggery wastewater was directly treated with a sequencing batch reactor (SBR) process, the efficiency was low with COD removal about 10% and NH4+ -N removal about 70%. The effluent COD concentration was higher than 1000 mg/L and effluent NH4+ -N concentration was 200 mg/L or so. The working state of the reactor was unstable and its performance deteriorated gradually during operation. After adding no-digested piggery wastewater (raw wastewater) to digested piggery wastewater in the influent, the reactor performance was significantly improved with COD removal higher than 80% and NH4+ -N removal up to 99%. The effluent COD concentration was in the range of 250 mg/L to 350 mg/L and effluent NH4+ -N concentration was lower than 10 m/L. The working stability of the reactor was greatly increased. After adding raw wastewater, the ratio of BOD5 to COD in the influent was raised from 0.19 to 0.54, and the ratio of BOD5 to TN was raised from 0.28 to 2.04, which implied an increase of carbon source for microbial growth and denitrification. The elevated denitrification resulting from the increase of carbon source not only promoted the removal of total nitrogen, but also stabilized the pH value by supplementing alkalinity to treatment system.