A vinyl 4-tetrahydropyranyloxybenzal-vinyl 4-hydroxybenzal-vinyl tetrahydropyranyl ether-vinyl acetate copolymer, a vinyl 4-tetrahydropyranyloxybenzal-vinyl tetrahydropyranyl ether-vinyl acetate copolymer and a preparation method thereof are provided. The copolymers have excellent transparency because they are very low in optical absorbance in the deep uv range. In addition, the acetal structure in the backbone and in the substituted groups endows the photoresist of the copolymer with superior dry etch resistance.