Abstract: Rational reflux or reuse of biogas slurry in rice straw anaerobic biogas digesters can reduce amount of the slurry to be discharged, thus lowering the cost of subsequent disposal of the slurry. For the purpose of providing scientific basis for modification of the technology of full reuse of biogas slurry, an experiment was carried out using rice straw as substance and a continuous stirred tank reactor (CSTR) to study effect of continuous full reflux of biogas slurry on anaerobic fermentation of rice straw in an attempt to elaborate mechanism of the effect. Results show that using continuous full reflux of biogas slurry, the reaction system ran stably for 50 days with TS, VS and volumetric biogas production rate stabilized at 245 mL·g^-1, 300 mL·g^-1 and 0.74 L·L^-1·d^-1, respectively. However, with the system running on till 85 days, though no apparent changes were observed in pH of the solution and volume fraction of methane in the digester, TS, VS and volumetric biogas production rate declined to 186 mL·g^-1, 226 mL·g^-1 and 0.56 L·L^-1·d^-1, respectively, or by around 24% as compared with their respective ones in the stable period. Further analysis shows that ammonia nitrogen in the slurry dropped to 185 mg·L^-1 or by 71% in concentration. Meanwhile, the total concentration of main metal ions rose up to 4.13 g·L^-1 or by 342%. Consequently, it can be preliminarily ascertained that continuous full reflux of biogas slurry would affect biogas production of the system, which may be attributed to the significant decrease in nitrogen content and accumulation of salts caused by full reflux of biogas slurry in the solution of the system. However, further efforts should be made to dig its real causes.