The invention discloses a novel rotary air-cooled grate system for a biomass boiler, which comprises a rotating shaft (1), a grate chassis (4), a chassis bracket (5), a grate (6), a primary air duct (7), an air duct bracket (8), a wind deflector (9), a belt pulley (10), a belt (11) and a motor (12). The novel rotary air-cooled grate system for the biomass boiler is characterized in that the rotating shaft (1) rotates to drive the grate (6) to rotate; and air enters the primary air duct (7) through the wind deflector (9) and is uniformly blown towards the grate (6), so that the fuel on the grate is combusted. The novel rotary air-cooled grate system for the biomass boiler has the advantages that firslty, a variable-speed gear can be manually adjusted, so that the grate is low and uniform in rotating speed, and the fuel is uniformly arranged on the grate and is fully combusted; secondly, the shaft and the bearing are cooled by the air, and the self-temperature is effectively reduced, so that the primary air temperature is raised, and the fuel is conveniently combusted; and thirdly, the air supply temperature is changed through the wind deflector, so that the primary air is uniformly blown to the grate; and therefore, the grate is cooled, and the phenomenon that the biomass ash drops on the bearing so as to damage the shaft and accessories is avoided.