The invention relates to a semi-
tower type medium-temperature separation 
biomass circulating fluidized bed boiler, composed of a front shaft, a middle gas-
solid separating and recycled material returning unit, and a 
tail flue, wherein the front vertical well comprises a 
hearth, a 
convection shaft and a 
smoke reversing chamber; the middle gas-
solid separating and recycled material returning unit comprises a gas-
solid separating device, a returning riser and a returning device; a super-heater, an 
economizer and an air pre-heater are arranged along a 
smoke flowing direction in the 
tail flue; a lower portion of the 
hearth is provided with 2 to 3 
layers of secondary air along a height direction; an upper portion of the 
hearth is provided with a 
convection heated surface in the 
convection shaft; the hearth, the convection shaft, the 
smoke reversing chamber, the gas-solid separating device, the returning riser and the returning device compose a main circulation loop. According to the invention, adaptability of fuels is wide; 
combustion efficiency is high; abrasion and 
corrosion for the heated surface is poor; temperature of the smoke at an inlet of the gas-solid separating device is within a range of 400-750 degrees centigrade so as to effectively prevent slagging, 
slag hanging, dusts gathering, ashes blocking, 
bed materials blocking and returning device blocking in the boiler.