The invention discloses a preparation method for an optical isomer namely 2R,4S,2'S-itraconazole. The optical isomer namely 2R,4S,2'S-itraconazole is characterized in that an X-ray powder diffraction pattern obtained by measuring with Cu-K alpha ray is described in a figure 1 in the specification. The crystal provided by the invention is single and has higher purity, better stability, high solubility, good pharmaceutical activity and high bioavailability. The crystal form provided by the invention has high stability, can maintain stability even under severe storage conditions, and does not change in subsequent preparation and storage of a preparation. The preparation method provided by the invention is simple, has low cost, and is easy to realize large-scale and industrial production. The optical isomer namely 2R,4S,2'S-itraconazole crystal form and pharmaceutical compositions containing the same can be used for resisting fungal infection, and is also an effective mTOR inhibitor, thereby being able to be used for treatment of a variety of tumors (like non-small cell lung cancer and prostatic cancer).