The invention belongs to the technical field of UV (ultraviolet) photosysthesis and discloses a UV (ultraviolet) based photocatalytic unsaturated vegetable oil base polyol and a preparation method and application thereof. The method includes: 1), synthesis of vegetable oil acid ester, namely adding an alkaline solution with organic alcohol into heated vegetable oil to obtain the vegetable oil acid ester after refluxing reaction; 2), synthesis of epoxy vegetable oil acid ester, namely adding a catalyst and an oxidizing agent into the vegetable oil acid ester in the step 1) to obtain the epoxy vegetable oil acid ester after reaction; 3), synthesis of the vegetable oil base polyol, namely adding a nucleophilic reagent, a solvent and the catalyst to the epoxy vegetable oil acid ester in the step 2) to obtain the epoxy vegetable oil acid ester after UV light irradiation and reaction. A polyol analogue is prepared by the aid of vegetable oil by adopting UV photocatalytic ring opening, the reaction action is moderate, short in time and high in speed, simpleness in aftertreatment is achieved, stringent conditions are avoided, and great reference significance for widening the application of natural oil products and improving added value is achieved.