Abstract: A moderate temperature UASB(Up-flow Anaerobic Sludge Bed) system was developed, in which the heat energy was supplied by burning biogas from itself as fuel, to treat wastewater on small-and medium-scale pig farm. Because the fermentation temperature in this system is higher and less variable with seasons than that in ordinary temperature UASB, it is characterized with high reaction velocity, good effect, high gas-producing rate and good stability. Research depending on practice covered how to select a reasonable temperature increase, how to adjust the wastewater-heating system, to keep energy balance and to estimate feasibility of this moderate temperature UASB system. Analysis based on calculation suggests a reasonable temperature control measure under Chongqing Climate. Research indicated that the moderate temperature UASB system will run well without extra energy supply in Chongqing and other area where annual temperature is above 14.2℃, and the fermentation temperature can be maintained above 28℃.