The invention relates to cadmium (II) coordination compound including 5-bromoniacin and a preparation method thereof. The chemical formula of the coordination compound is [Cd(L)2]infinite, wherein L is the deprotonated 5-bromoniacin anion ligand of carboxyl. The synthesis method of the coordination compound comprises the steps of: placing the cadmium (II) metal salt at the bottom layer of a glasstest tube under the normal pressure and temperature, and adding distilled water for dissolution; adding the mixture of methanol and water thereupon as a buffer layer; adding a methanol solution of 5-bromoniacin ligand (HL) to the uppermost layer; and standing for a plurality of weeks to obtain the coordination compound of the invention. The coordination compound has good thermal stability, and the synthesis method thereof has the advantages of simple and convenient operation, high yield, good reproducibility, and the like. The invention is hopeful to be widely applied in the field of fluorescent crystal materials.