Combined with Suffer software analysis and by collecting and testing water samples in duck breeding area and surrounding water in two seasons of summer and winter, this paper studied the spatial-temporal variations in the water quality in the duck farms and its diffusion & reduction characteristics of the wastewater in Baiyangdian Lake in order to protect the ecological environment of Baiyangdian and reasonably plan the scale and range of duck breeding. The results showed that the water quality of duck breeding area were worse than class V of Surface Water Environmental Quality Standard(GB3838—2002), the main pollutants were total nitrogen, total phosphorus, ammonia nitrogen and chemical oxygen demand; the concentrations of these pollutants were 9. 51~14. 20 mg/L, 0. 92~1. 77 mg/L, 7. 33~9. 06 mg/L and 54. 10~83. 45 mg/L, respectively. And the pollutant concentration in summer was significantly higher than that in winter. The reduction effect of duck farm wastewater in the south of Baiyangdian Lake area is obviously better than that in North, mainly because the southern part of the lake has a wide surface of water and a wide distribution of aquatic plants, which is beneficial for the self purification of the Lake. The reduction efficiency of copper was the highest, 15. 5%/km±11. 0%/km in summer and 14. 8%/km±12. 9%/km in winter respectively. and the reduction efficiency of nitrate was the lowest, 8. 7%/km±5. 8%/km in summer and 5. 0%±4. 3%/km in winter respectively. The reduction efficiency of main pollutants decreased with the diffusion distance, which means the reduction efficiency of copper decreased fastest with the increase of diffusion distance while the nitrate was the slowest.