The invention relates to a biomass combustion furnace which comprises a furnace body and a hopper arranged behind the furnace body, and is characterized in that the furnace body is formed by splicingan upper furnace body and a lower furnace body, the splicing mode can be welding, riveting bolt fixing and the like, and a combustion chamber main body is arranged in the center of the lower furnace body; a discharging channel is installed at the bottom of the hopper and is arranged obliquely, a bottom end outlet of the discharging channel is located at the bottom of an inner cavity of the combustion chamber main body, and the upper end of the discharging channel penetrates through the side wall of the upper furnace body; a multi-stage gasification head is installed in the center of the upperfurnace body, is located at the top of the combustion chamber body and is matched with a multi-stage gasification head cover to form an internal gas channel, and the air enters a cavity channel defined by an upper annular plate, an upper lug plate, an outer wall, a lower annular body, a lower lug plate and a gasification pipe from a gas inlet on the lower lug plate and then is blown out from a round hole on the gasification pipe. By arranging the reasonable furnace body structure, the combustion efficiency is improved.