Provided are a separation method for easily recovering normal butene from an olefin fraction including isobutene, isobutane, 1-butene, 2-butene, and normal butane, and a separation process system using the method. Since the separation method according to the present invention may easily convert 1-butene included in the olefin fraction to 2-butene, normal butene may be effectively separated and recovered by factional distillation and each recovered fraction may be easily refluxed even if the use of a reflux system using a refrigerant is reduced or excluded. Thus, economic efficiency may be improved and simultaneously, separation efficiency may be increased.