The invention discloses a biomass pyrolysis furnace with detachable vertical semicircular tubes, and relates to the technical field of biomass pyrolysis furnaces. The biomass pyrolysis furnace comprises a feeding zone, a preheating zone, a carbonizing zone and a cooling zone which are sequentially arranged from top to bottom in the vertical direction. The two opposite semicircular vertical tubes, which vertically penetrate the pretreating zone, the carbonizing zone and the cooling zone, are arranged in the pretreating zone, the carbonizing zone and the cooling zone. Horizontal internal semicircular furnace pore plates are arranged at joints among the feeding zone, the preheating zone, the carbonizing zone and the cooling zone and at the bottom of the cooling zone. Pneumatic stop valves are arranged at positions, corresponding to the joint between the carbonizing zone and the cooling zone and to the bottom of the cooling zone, in the two semicircular vertical tubes. A preheating flame path, a carbonizing flame path and a cooling water path are sequentially arranged at positions, corresponding to the preheating zone, the carbonizing zone and the cooling zone, of a zone between the inner wall of a furnace body and the outer walls of the two semicircular vertical tubes. Two preheated air outlets communicated with the semicircular vertical tubes are arranged on the upper portion of one side of the preheating zone. The preheating flame path and the carbonizing flame path are communicated through a U-shaped pipe arranged on the outer wall of the furnace body. Two carbonized gas outlets communicated with the semicircular vertical tubes are arranged at the top of one side of the carbonizing zone. Baffle plates are arranged in the preheating flame path, the carbonizing flame path and the cooling water path. The biomass pyrolysis furnace has the advantages that the preheating zone and the carbonizing zone are arranged independently, the purity of target products can be improved, and high-quality biochar can be obtained through the semicircular vertical tubes and the baffle plates.