NOVELTY - The device has a gas dryer (6) whose air outlet connector is connected with an air inlet connector of a roots fan (7) via a first gas pipe. The roots fan is mounted on a proper position of a sewage-collecting box (1). An air outlet connector of the roots fan is connected with a water seal cabinet via a second gas pipe. An air inlet connector of the water seal cabinet is connected with the air outlet connector of the roots fan via the second gas pipe. The air outlet connector of the water seal cabinet is connected with a gas storage tank at an outer side of the device via a third gas pipe.    USE - Integrated fuel gas purifying device for preparing gas by a biomass.    ADVANTAGE - The device precipitates dust, tar and wood vinegar discharged into the sewage-collecting tanks for being discharged into an external precipitate purifying pond in a uniform manner and purified in a precipitating way while using again. The device occupies less space and reduces civil work amount. The device is simple, reasonable and compact in structure, simple in technique and safe to use, and has high efficiency and strong practical applicability, and requires short pipeline, less pipeline connecting piece and small maintenance quantity and avoids blockage. The device reduces leakage and integrates spraying, washing, centrifuging and dust collecting functions. The device ensures combining temperature-lowering, filtering and purifying functions. The device ensures high purity, high heat value and complete combustion of filtered and purified combustible gas. The device saves energy, and is environmental-friendly. The device comprises a tar content in the combustible gas, which is lower than national standard.    DETAILED DESCRIPTION - The sewage-collecting box is a steel structural rectangular box.    DESCRIPTION OF DRAWING(S) - The drawing shows a side view of an integrated fuel gas purifying device in partial section.    Sewage-collecting box (1)    Spray device (2)    Cyclone dust collector (4)    Centrifugal dust collector (5)    Gas dryer (6)    Roots fan (7)