Abstract: In order to evaluate the operation of anaerobic fermentation system，ten large-scaled pig farms were selected in Guangdong province to monitor the contents of nitrogen and phosphorus in sewage discharged from the hoggery and methane tank. The results showed that anaerobic fermentation system effectively decreased the content of nitrate nitrogen and nitrite nitrogen of hoggery sewage，and the reduction rates of 19.89%-59.02% and 18.75%-83.97% （2# excluded）were observed for nitrate nitrogen and nitrite nitrogen，respectively. The anaerobic fermentation system in several pig farms did not performed well in total nitrogen，ammonium nitrogen and total phosphorus as evidenced by the increase of these index in sewage of methane tank. The reduction rates of total nitrogen，ammonium nitrogen and total phosphorus were -49.18%-43.14%，-83.72%-21.07% and -13.89%-52.82%，respectively. Sewage discharged from the methane tank received further treatment by the fish pond and oxidation pond and then discharged out of the pig farm. The concentration of NO2 --N and NO3 --N in effluent of pig farm increased significantly，compared to that in effluent of methane tank，whereas the concentration of TN，NH3-N and TP in effluent of pig farm decreased sharply in contrast with the effluent of methane tank. However，the TP content in effluent of ten farms all exceeded the value of the discharge standard of pollutants for livestock and poultry breeding，which would pose a pollution potential to surrounding environment.