Cassava-based ethanol-methane coupled system is a novel cleaner ethanol production process in which the anaerobic digestion effluent is recycled to the next batch of ethanol fermentation process.However ammonia generated from the anaerobic digestion could be accumulated with the recycling and thus resulted in reduction of ethanol production due to Maillard reaction between ammonia and reducing sugar.Therefore the technology of centrifugation and ventilation were utilized to control the ammonia nitrogen.Control process and regulation process were designed to study accumulation and regulation of ammonia nitrogen and its influence on the process.Results showed that the ammonia nitrogen concentration increased to 811 mg/L after seven cycles of fermentation,and the ethanol fermentation was inhibited with obvious reduced ethanol production when the ammonia nitrogen concentration reached 550 mg/L in the control process.Such phenomenon did not occur in the process with ammonia nitrogen regulation,where the ammonia nitrogen concentration maintained at the level of approximately 350 mg/L.Ammonia nitrogen caused the accumulation of alkalinity in control process indirectly,but other parameters on methane fermentation were normal.Regulation process guaranteed the ethanol production and performance of the system.