The invention provides a method for fractionating mixing hydrocarbons. The mixing hydrocarbon raw material enters a fractionating tower, the fraction, of which the distillation range is more than 350 DEG C, is drawn out from the bottom of the fractionating tower; and first material current is drawn out from the middle-lower part of the fractionating tower, and is subjected to steam stripping in a first steam stripping tower to obtain the fraction of which the distillation range is between 250 and 360 DEG C; second material current is drawn out from the middle-upper part of the fractionating tower, and is subjected to steam stripping in a second steam stripping tower to obtain the fraction of which the distillation range is between 160 and 260 DEG C; and the oil gases exhausted from the top of the fractionating tower are subjected to condensation cooling separation to obtain rich gases and liquid, wherein the liquid is subjected to steam stripping in a third steam stripping tower to obtain C5<-> fraction and C6<+> fraction. The method aims at the special needs of the process on producing micromolecule hydrocarbons and aromatic hydrocarbons to the maximum extent to provide cracking materials for the process, and realizes the fine separation by the arrangement of three steam stripping towers of light aromatic hydrocarbon materials, heavy aromatic hydrocarbon materials and remixing materials, thereby improving the separation precision.