The invention discloses a preparation method of a sulfur dioxide, carbon dioxide and epoxide copolymer. According to the method, epoxide, SalenCr<III>Cl and PPNCl are sequentially added to a high-pressure reaction kettle, sulfur dioxide and carbon dioxide are introduced and have a reaction at the temperature of 50-100 DEG C for 8-48 h, then, a product is dissolved with chloroform, a hydrochloric acid and methanol solution is used for precipitation, amber precipitates are filtered and repeatedly washed with methanol, the washed product is dried in vacuum at the room temperature, and the sulfur dioxide, carbon dioxide and epoxide terpolymer with higher stereoregularity can be obtained. The sulfur dioxide, carbon dioxide and epoxide terpolymer has structural characteristics of polycarbonate and polysulfone and has a wide application prospect in the fields of packaging, filtration and the like; the preparation method is simple, few catalysts are used, the reaction temperature is mild, the yield is high, the structure regularity of the product is good, the cost is low, and industrial production is easy to realize.