Abstract: To study the digestion ability of biogas slurry in paddy field and the potential risk of water environment pollution in the process of digestion, 4 irrigation amounts of biogas slurry treatments and 2 control treatments were designed based on the location test with engineering measures in this study. The treatments included 1000 t/hm2 biogas slurry at base-tiller stage of rice combined with 120 kg/hm2 nitrogen (urea) at panicle stage of rice (BS10), and 635.29, 423.53, 211.76 t/hm2 biogas slurry at base-tiller stage respectively combined with 423.53, 282.35, 141.18 t/hm2 biogas slurry at panicle stage (300% BS, 200% BS and 100% BS). The control treatments were conventional fertilization (CF) with 180 kg/hm2 nitrogen (urea) at base-tiller stage and 120 kg/hm2 nitrogen (urea) at panicle stage, and no-fertilization treatment (CK) without fertilizer both at base-tiller stage and at panicle stage of rice. Then the changes of the total nitrogen, ammonia nitrogen and nitrate nitrogen in both field surface water and soil percolation water at 40 and 60 cm depth were monitored 1, 2, 3, 5 and 7 d after biogas slurry application during the main rice growth period. The data were analyzed by Microsoft Excel (2010) and SPSS for windows (13.0). Results showed that: 1) The key period of biogas slurry digestion in paddy field was the first 3 d after irrigation with the total nitrogen degradation rate of 46.67%-78.36% and the ammonia nitrogen degradation rate of 47.52%-85.27%. And the digestion rate at panicle fertilizer stage was greater than that at base-tillers stage. The environmental risk of surrounding water body eutrophication was bigger if runoff was generated 3 d after the irrigation. To ensure safe disposal and realize the reduction of agricultural non-point source pollution source and emissions, engineering measures should be adopted such as closing field drain or increasing ridge height by 5-10 cm to control surface runoff. 2) The potential risk of surrounding water pollution with the amount of biogas slurry digestion above the 200% BS processing (i.e., 705.88 t/hm2) was higher than the conventional fertilization treatment both at base-tillers stage and at panicle fertilizer stage. Compared with the conventional fertilization treatment, 100% BS processing (i.e., 352.94 t/hm2) had a lower potential risk of environmental pollution. Therefore, the biogas slurry digestion in paddy field should adopt the way of more irrigation times and fewer disposal amounts. 3) To resolve the pollution risk to soil percolation water from biogas slurry digestion in paddy field with engineering measures was mainly concentrated in the tillers stage, and the ammonia nitrogen pollution risk was the main risk while the nitrate pollution risk was less. The pollution was different among different water penetration depths. Research indicated that the safe disposal amount of biogas slurry at a time in tillers stage should be controlled below the amount of 211.76 t/hm2, and less than 423.53 t/hm2 in panicle fertilizer stage. These results can provide a theoretical reference for the technology of biogas slurry safe disposal in paddy field and the technology of reducing emission in agricultural non-point source pollution from source.