A method for preparing a Rivaroxaban intermediate I is presented, including the following step: in a non-protonic solvent, under the effect of lewis acid, performing cyclization reaction on 4-(4-phenyl isocyanate)morpholine-3-ketone (II) and (S)-epoxy compound (III), the reaction temperature ranging from 20° C. to 60° C., where R is amino replaced by amino protecting group. The preparation method of the present invention has a mild condition, a simple process, a low cost, and high efficiency; the product is easy to purify and the method is applicable to industrial production.