The invention discloses a method for preparing cyclic carbonate by transforming a copper-based catalyst into carbon dioxide. Carbon dioxide and epoxide serve as raw materials, a conjugate copper porphyrin microporous polymer material serves as a heterogeneous catalyst, tetra-n-butylammonium bromide serves as a co-catalyst, and efficient green catalytic synthesis of cyclic carbonate is realized atnormal temperature and pressure in a solvent-free manner. The method mainly has the advantage that the catalyst is simple in preparation method, low in cost, high in catalytic activity, stable in structural performance, easy to recycle, reusable, mild in reaction condition, high in speed, safe to operate and applicable to large-scale industrial production.