A fluidized bed regenerator, a device for preparing low-carbon olefins, and a use thereof are provided. The fluidized bed regenerator includes a second activation zone, a first activation zone, and a gas-solid separation zone from bottom to top; the second activation zone axially communicates with the gas-solid separation zone; the first activation zone is arranged on a periphery of a junction between the second activation zone and the gas-solid separation zone; the first activation zone is an annular cavity; n baffles are radially arranged in the first activation zone, and the n baffles divide the first activation zone into n first activation zone subzones; and a catalyst circulation hole is formed in each of n−1 of the baffles such that a catalyst entering the first activation zone flows in an annular direction.