Abstract: The present disclosure belongs to the technical field of nanomaterial synthesis, and in particular, to a preparation method for a narrow-linewidth alloy quantum dot. The preparation method provided by the present disclosure includes the following steps: in a protective gas atmosphere, mixing a cadmium source, an organic ligand, and an organic solvent with a first selenium source for a nucleation reaction to obtain an organic solution of a CdSe quantum dot core; and mixing the organic solution of the CdSe quantum dot core, a zinc source and an inorganic anion source for shell coating to obtain the narrow-linewidth alloy quantum dot, where the inorganic anion source includes a second selenium source.