The invention relates to a special polyolefin resin modified composition for rotational molded products and a preparation method thereof, belonging to compositions of polyolefin homopolymers or copolymers. The special polyolefin resin modified composition is characterized by being prepared from the following raw materials in parts by weight: 50-80 parts of carrier resin, 10-45 parts of heterogeneous nucleating agent, 0.5-2 parts of master antioxidant, 0.5-2 parts of secondary antioxidant, 0.5-2 parts of anti-ultraviolet agent, 0.5-2 parts of surface treating agent and 0.5-3 parts of dispersing agent. The special polyolefin resin modified composition for rotational molded products and the preparation and use methods thereof, provided by the invention, have the advantages that the crystallization rate of a rotational molded product preparation process can be controlled and adjusted, the dimensional stability of the products is improved, and the products are smooth in inside/outside surface, uniform in wall thickness, long in service life and excellent in comprehensive performance and are free from the defects of obvious distortions, pits and bubbles; the deformation of the products can be decreased by 50%, the production time is shortened by over 30%, and the dimensional stability is improved by more than 1 times.