The invention discloses a circulating fluidized bed boiler, which belongs to the technical field of thermal power equipment. The circulating fluidized bed boiler consists of an v-shaped hearth, separators, tail flues, a water cooled wall, a middle membrane-type wall, a ribbed plate membrane-type wall, a U-shaped wall and headers, wherein the separators and the tail flues are symmetrically distributed on two sides of the hearth; the middle membrane-type wall divides the hearth into two completely symmetric parts to prevent a bed from titling; the upper part of the middle membrane-type wall is provided with a vent hole to maintain the pressure balance of the hearth; and the airflows in the U-shaped wall flow alternately to reduce the heat difference in the hearth. The circulating fluidized bed boiler avoids the bed tilting phenomenon in the v-shaped hearth of the circulating fluidized bed boiler, has the characteristics of uniform temperature distribution in the hearth and high safety and is a better circulating fluidized bed boiler which is particularly adaptable to the development trend of large circulating fluidized bed boilers.