The utility model discloses a sleeve type sand seal three-way expansion joint for a slag discharge pipe of a fluidized bed boiler. The expansion joint comprises an outer sleeve pipe and an inner sleeve pipe inserted into the outer sleeve pipe, wherein, the upper part of the outer sleeve pipe is covered by a movable ring-shaped seal plate; a ring-shaped sand seal groove is filled with fine sand; the outer sleeve pipe and the inner sleeve pipe form a sleeve type structure, so that the inner sleeve pipe can smoothly expand and shrink by 150mm in the outer sleeve pipe; the movable ring-shaped seal plate moves horizontally along with three-way expansion and shrinkage of the inner sleeve pipe and does not move vertically; and the fine sand in the ring-shaped sand seal groove reliably seals outward escape of gas in slag and the spraying of slag particles by relying on the gravity force. The expansion joint solves the problem of three-way expansion and the sealing of the slag discharge pipe of the fluidized bed boiler, and simultaneously solves the problem of poor sanitary condition of the surrounding environment of cold slag equipment.