The invention discloses a coumarin derivative and preparation and application thereof. 7-hydroxy-4-methyl coumarin as a raw material is subjected to substitution reactions with halogenated ethyl alcohol and 4-vinylbenzyl chloride in sequence, and then 7-[2-(4-vinyl benzyloxy)-ethyoxyl]-4-methyl coumarin is obtained. The method has the advantages that the operation is simple, the conditions are mild, the product is easy to purify, and the yield is high, the coumarin derivative synthesized by using the method has polymerizable double-bond elements, alkoxy flexible spacers and coumarin photosensitive groups, and when the coumarin derivative as a photosensitive monomer used for synthesis of a photostimulation response polymer material, the polymerization efficiency can be obviously improved. The water solubility and the degradability of the polymer material synthesized by using the counmarin derivative can be improved, the hydrophily and the hydrophobicity of the polymer material are moreeasily regulated and controlled, and therefore, in the use process of the polymer material as a drug carrier, the drug encapsulation and release rates can be better controlled.