The invention relates to an application of a compound RA in preparing brivaracetam intermediate chiral butyrolactone. The compound RA splits a compound BW-CX chirally to obtain BW-C as shown in a formula. When the compound RA is applied to prepare the brivaracetam intermediate chiral butyrolactone, splitting of a chiral column is not needed, so that the process flow is simple, and the shortcomingthat brivaracetam is hardly produced on a large scale in an existing process is overcome.