NOVELTY - A biomass gasifier comprises furnace body (1) comprising furnace cover (11), annular gasifying agent preheating chamber (3), furnace box (32), ash box (24), transmission case (15), central shaft (5), furnace body plate (20), dynamic seal device (25), bracket (9), steam generator (2), inlet tube (2-1), outlet tube (2-2), gasifying agent input tube (27), nozzles (3-1); bias tower distribution air furnace disk (4), distribution air orifices (4-1), and stirring and pressing arm (6).    USE - The biomass gasifier is useful as biomass gasifying device (claimed).    ADVANTAGE - The biomass gasifier has long gas generating time, steady and continuous work, does not die out in the middle process, protects environment, saves energy, is anti-blast, and has high heat substance; it has simple structure and low manufacturing cost.    DETAILED DESCRIPTION - A biomass gasifier comprises furnace body (1) with furnace cover (11); wherein an annular gasifying agent preheating chamber (3) at the lower end of the furnace body (1) divides the cavity into a furnace box (32) and an ash box (24); the lower end of furnace body (1) is equipped with transmission case (15); the output shaft of the transmission case is the central shaft (5) of the furnace body; the central shaft (5) is connected with the furnace body plate (20) through the dynamic seal device (25); the upper end of the central shaft (5) is fixedly connected with the bracket (9) inside the furnace box (32); the inner ring bracket of the gasifying agent preheating chamber (3) is fixedly connected with steam generator (2); the lower end of the stream generator (2) is equipped with inlet tube (2-1) where upper end is equipped with outlet tube (2-1), and the inlet tube (2-1) and the outlet tube (2-2) are fixedly connected on the furnace body (1); the gasifying preheating chamber (3) passes through the central shaft (5), is connected with the outlet tube (2-2) of the steam generator (2), and has connection with the gasifying agent input tube (27) in cutting line direction; the inner ring of the gasifying agent preheating chamber (3) is equipped with multiple nozzles (3-1); the central shaft (5) located above the gasifying agent preheating chamber (3) is fixedly connected with bias tower distribution air furnace disk (4) which is non-symmetrically shaped as ladder hollow structure with the central shaft (5); the wall of the bias tower distribution air furnace disk (4) is equipped with multiple distribution air orifices (4-1); the central shaft (5) is crossly equipped with semi-circular spirally distributed stirring and pressing arm (6); the upper end of the furnace body (1) is equipped with gas orifice.    DESCRIPTION OF DRAWING(S) - The drawing the shows the cross-sectional view of the biomass gasifier.    Furnace body; (1)    Annular gasifying agent preheating chamber; (3)    Furnace cover; (11)    Ash box; and (24)    Furnace box (32)