The invention discloses a preparation method of perovskite single crystals. The perovskite single crystals are CsPbBr3 perovskite single crystals or CsPb2Br5 perovskite single crystals, and the perovskite single crystals are in the shape of sheet or rod. A preparation method comprises the following steps: cleaning a single crystal growth substrate, wherein respectively carrying out ultrasonic treatment on the substrate for 15-30 minutes with acetone, 70%-80% ethanol and deionized water, taking out the substrate, and drying the substrate in a drying oven overnight to obtain a single crystal growth substrate; preparing a perovskite precursor solution, wherein dissolving CsBr and PbBr2 in hydrobromic acid or dimethyl sulfoxide according to the proportion of 1/1-1/4, controlling the concentration of CsBr to be 0.06 mol/L to 0.3 mol/L, the concentration of PbBr2 to be 0.06 mol/L to 0.3 mol/L, and obtaining a perovskite precursor solution; and preparing the perovskite single crystals, namelypreheating the perovskite precursor solution to 80-95 DEG C, dripping the perovskite precursor solution on the substrate, and removing the solvent to obtain the perovskite single crystals. The methodis simple to operate and low in operation process difficulty, and the components and morphology of the perovskite single crystals are adjustable.