The utility model discloses a circulating fluidized bed cyclone separator and a center cylinder mounting structure thereof. The mounting structure comprises a center cylinder body (1), a first supporting ring (2) and a second supporting ring (3) connected to a peripheral surface of the center cylinder body (1), a first stiffener plate (4), a support frame (5) which supports the bottom surface of the first supporting ring (2), multiple stiffeners (6) of which one ends are connected to the peripheral surface of the center cylinder body (1) and the other ends are inserted into the support frame (5), and a limiting plate (7) connected to the other end of each stiffener (6). In addition, the utility model also discloses a circulating fluidized bed cyclone separator comprising the circulating fluidized bed cyclone separator center cylinder mounting structure. The circulating fluidized bed cyclone separator center cylinder mounting structure is hard to deform in a high-temperature state, and the problem that the center cylinder deviates, wholly drops or sinks can be solved.