The invention relates to combustion furnaces and provides a biomass combustion furnace which is suitable for heating heat transfer oil furnaces, superheated steam furnaces, air heating furnaces, water heaters and the like. Through the biomass combustion furnace, biomass can be enabled to be combusted sufficiently, utilization rate of biomass combustion is increased, combustion ash can be removed timely during combustion, and pollution due to the fact that air flow is discharged into air is avoided. The biomass combustion furnace comprises a combustion base, a combustion chamber arranged on the combustion base and a flange arranged on the combustion chamber, the combustion base comprises a combustion base body, a feed device and a second air blower, an ash storage box is arranged at one end of the combustion base body, an air inlet box is arranged at the other end of the combustion base body, a combustion tank which is communicated with the ash storage box and the air inlet box is arranged on the upper portion of the combustion base body, air vents are formed in the combustion tank, the combustion tank, the bottom surface and the lateral surface of the combustion base body, the ash storage box and the air inlet box form a cavity jointly, an air inlet communicated with the air inlet box is formed in the lateral surface, connected with the air inlet box, of the cavity, the feed device is arranged outside the combustion base body and passes through the air inlet box to be led to the combustion groove, and the second air blower is communicated with the air inlet box.