The invention discloses a preparation method of a CsPbBr3 perovskite three-dimensional cube microcavity sample. The preparation method comprises weighing CsBr and PbBr2 powders, putting the CsBr and PbBr2 powders in a flat quartz boat, putting the flat quartz boat into a quartz tube of a tube furnace, putting a sedimentary sheet in the quartz tube of the tube furnace and in an air outlet of the quartz tube; raising the temperature of the furnace under the protection of nitrogen to 600 DEG C, and reacting, wherein a yellow sediment on the sedimentary sheet is the CsPbBr3 perovskite three-dimensional cube microcavity sample. The surface of a prepared CsPbBr3 three-dimensional cube perovskite microcavity is smooth, the size of the three-dimensional cube microcavity is 1-15 mum, the size and the height are adjustable, and the preparation method has the excellent characteristics of convenient operation, high repeatability, high crystalline quality, controllable morphological size and height, etc.