Abstract: The fluidized bed gasifier system was developed and the swine manure air-gasification experiments were carried out. The effects of particle size and start-up temperature on gasification process were studied. The experiments showed the feedstock particle size would influence the solid residence time and contact area in the gasifier. The high temperature field was upper shift with increasing of particle size which required the reactor had enough fluidization height to ensure the solids residence time. The gas highest production rate appeared to 0.5 mm particle size. Solid yield decreased and liquid yield increased with increasing particle size. There had no obvious effects on the composition of gaseous products within 1 mm particle size. Three gasification indexes of fuel gases calorific value, carbon conversion and gasification efficiency were calculated and the 0.5 mm particle size had the best results. The experiments also showed that the higher start-up temperature was, the shorter reactor startup time was, which was beneficial to gaseous production. The yield of liquid products decreased with increasing start-up temperature and the solid production had no fluctuation because of the constant equivalence ratio (ER). The content of some small molecules gases increased with rising of start-up temperature, which was contrary to those of some macromolecules gases. The experiments also showed the start-up temperature had no obvious impacts on the three gasification indexes.