A selenium-rich enhancer for plant cultivation and preparation and application thereof. The selenium-rich enhancer contains: an organic selenocyano-compound. The organic selenocyano-compound is selected from one or a combination of the compounds of the structure of Formula I or Formula II, Formula I: R—SeCN, wherein, R is alkyl or aromatic groups and Formula II: (R—SeCN)nA, wherein, R is alkyl or aromatic groups, n is an integer of 1-5, and A is a cation. The selenium-rich enhancer is employed to cultivate plants by utilizing the organic selenocyano-compound, and the survival rates, yields and organic selenium contents of plants are all improved. When pepper is planted by using that, the selenium content can reach more than 180 μg/kg.
