The invention discloses a large biomass boiler which comprises a boiler body. The large biomass boiler further comprises a hearth, a boiler circle, an ash discharge device, an ash collection box, a stock bin, a spiral feeding device, a waste heat recycling chamber, a waste heat water tank, a first smoke dust filter device, a second smoke dust filter device, a first fan, a second fan, a third fan and a controller which are matched with the boiler body and assembled into a whole. A fire stop ring is arranged above the hearth and located below the boiler circle, a fire grate is arranged inside the hearth, and the lower end of the hearth is provided with an ash discharge hopper. Smoke residual heat is utilized more sufficiently, the waste heat utilization efficiency is improved, the efficiencyis high, energy is saved, waste gas is exhausted after being filtered to reach standards, environmental protection is better, fuel ignition time is shorter, ash removal operation can be automaticallycompleted, manual treatment is not needed, the working efficiency is high, biomass fuel combustion is more sufficient, and combustion time is longer.