NOVELTY - A gasifier comprises a first gasifying hearth box; a second gasifying hearth box; and a gasifier body. A gasifier body comprises a roof binder (45), an inlet orifice (38), a synthesized gas outlet (1), a branch air chamber (2), the overheat cavity, a motherboard (24), flame-resistant liners (5, 35), a heat-insulating layer (6) and an outside shell (7). The first and second hearth boxes are each surrounded by the flame-resistant liner.    USE - A gasifier for trash and biomass (claimed).    ADVANTAGE - The gasifier has increased efficiency by gasifying trash and biomass via two gasifying hearth boxes; improves the quality of synthesized gas; eliminates tar and virulent dioxin; reduces pollutant in the synthesized gas; facilitates purification; and can transform waste and biomass into valuable synthesized gas including city gas product used for producing hydrogen, methanol and dimethyl ether.    DETAILED DESCRIPTION - A gasifier comprises a first gasifying hearth box surrounded by a flame-resistant liner (35); a second gasifying hearth box surrounded by a flame-resistant liner (5); and a gasifier body. An overheat cavity (4) is set in the flame-resistant liner of the second gasifying hearth box. A baking area (VII), a pyrogenation area (VI), an oxidization area (V) and a reduction area (IV) are coaxially arranged in the first gasifying hearth box. A plasma gasification area (III), a detention area (I) and a burning area (II) are arranged in the second gasifying hearth box. The plasma gasification area is installed at the bottom. The detention area is above the plasma gasification area. The burning area is on a lower part of one side of the plasma gasification area. Bottoms of the first and second gasifying hearth boxes are connected directly. A gasifier body comprises a roof binder (45), an inlet orifice (38), a synthesized gas outlet (1), a branch air chamber (2), the overheat cavity, a motherboard (24), the flame-resistant liners, a heat-insulating layer (6) and an outside shell (7). The roof binder is equipped on the top of the first gasifying hearth box. An inlet orifice (38) is located on an upper part of the first gasifying hearth box. The synthesized gas outlet is opened on the top of the second gasifying hearth box. The branch air chamber and the overheat cavity are set and connected in the second gasifying hearth box. The motherboard is set at the bottoms of the first and second gasifying hearth boxes. One of the flame-resistant liners, the heat-insulating layer and the outside shell comprise a wall of the first gasifying hearth box. One of the flame-resistant liners, the heat-insulating layer and the outside shell comprise the wall of the second gasifying hearth box.    DESCRIPTION OF DRAWING(S) - The drawing is sectional view of the gasifier.    Synthesized gas outlet (1)    Branch air chamber (2)    Overheat cavity (4)    Flame-resistant liners (5, 35)    Heat-insulating layer (6)    Outside shell (7)    Motherboard (24)    Inlet orifice (38)    Roof binder (45)    Detention area (I)    Burning area (II)    Plasma gasification area (III)    Reduction area (IV)    Oxidation area (V)    Pyrogenation area (VI)    Baking area (VII)