The invention provides a preparation method of a fully inorganic perovskite quantum dot and relates to the technical field of material preparation. The method comprises the following steps: mixing 110to 145 mg of metal halide and 2.5 to 32 mg of Cs compound, adding 5 to 150 mL of octadecene, 0.2 to 2 mL of amine organic matter and 0.2 to 2 mL of oleic acid to prepare a solution, performing reaction at 80 to 110 DEG C for 0.2 to 2 hours, adding 10 to 15 mL of a precipitating agent, centrifuging, removing supernatant liquid, adding 10 to 15 mL of a dispersing agent and drying to obtain the solution of the fully inorganic perovskite quantum dot. The method needs low reaction temperature, does not need inert gas protection, and is simple in preparation process and suitable for large-scale production.