The invention provides a controllable-molecular-weight high-refraction resin and an environment-friendly preparation method thereof. According to the preparation method, the addition reaction capable of avoiding generating small molecule byproducts is adopted, and the raw material charging sequence and proportion are rationally designed to control the molecular weight of the product, thereby structurally implementing the control on the resin properties. The resin product has high refractivity, and can be used in spectacle lenses, optical lenses, building materials and other fields with requirements for refractivity. The structural general formula of the resin provided by the invention is disclosed as Structure I.