The invention discloses a separation method for mixed C4, which comprises the following steps of separating butene and butane from mixed C4 through extractive distillation, wherein the mixed C4 contains n-butane, iso-butane, 1-butylene and 2-butylene after removal of components such as C3, butadiene, alkyne, isobutene, C5 and the like, furthermore, separating to obtain iso-butane, 1-butylene and 2-butylene and the byproduct of crude n-butane through ordinary distillation, wherein the solvent for extractive distillation is publicly known in the industry, non clear-clear separation method is adopted in extractive distillation technology, namely, the combination of preextraction distillation and extractive distillation. Due to the adoption of the separation method, after the mixed C4 is processed, products of iso-butane, 1-butene and 2-butene of high concentration can be obtained simutaneously, therefore, the separation method has the advantages of being energy-saving, good in economic efficiency, high in resource utilization rate, and the like, reducing the cost and is of great significance in comprehensive utilization of mixed C4 resource.