The invention relates to a preparation method of hexagonal-phase CsPbBr3 nanocrystalline. The preparation method comprises the steps of uniformly dispersing lead bromide powder in an N, N-dimethylformamide solution, carrying out stirring under a water bath condition to completely dissolve the lead bromide powder to obtain a lead bromide precursor solution; uniformly dispersing cesium bromide powder in an absolute ethyl alcohol solution, and carrying out stirring under a water bath condition to completely dissolve the cesium bromide powder to obtain a cesium bromide precursor solution; and simultaneously injecting the lead bromide precursor solution and the cesium bromide precursor solution into a chloroform solution at room temperature under a stirring condition, standing after continuousstirring, and centrifugally separating solids in the product to obtain the hexagonal-phase CsPbBr3 nanocrystalline. The N, N-dimethylformamide solution is a mixed solution of oleylamine, oleic acid and N, N-dimethylformamide; and the absolute ethyl alcohol solution is a mixed solution of the oleylamine, the oleic acid and the absolute ethyl alcohol. Compared with the prior art, the preparation method has the advantages that the preparation method is simple to operate, the stoichiometric ratio of elements is controlled accurately, high-temperature or inert gas protection devices are not required, and the like.