The wastewater from paper making with recycled fiber was treated with Up-flow Anaerobic Sludge Bed(UASB).Digestion sludge of municipal wastewater plant was used to start the UASB system.The COD of the wastewater was about 1?100?mg/L,which was close to the property of the wastewater of most paper mills using recycled fiber.The HRT of UASB reactor was about (4.43?h),which accorded with most UASB plants.During the research,the starting up and operating process of the UASB reactor were observed.The temperature of the water,the VFA and alkalinity concentration of the UASB effluent was surveyed particularly.The UASB reactor was found to keep high treatment efficiency by adjusting the load of the UASB and supplying N,P elements and some other microelements.The process removed about 90% of COD,50% of total hardness,and 80% of sulfate on average.The main factors affecting the treatment efficiency were temperature,nutriments and the sludge exposure level to substrate.Especially,the temperature had a close relationship with the methane yield rate.The relation could be given with the Arrhenius equation.