In order to effectively reduce flow distortion produced in the S-shaped inlet, a computational fluid dynamics (CFD) procedure was used to design vortex generator installations near the entry of the diffuser. Several parameters, i.e. the ratio of generator blade height to local boundary layer thickness, the locating position, angle against the centerline, that characterize the vortex generator array were discussed to determine their effects. Especially the numbers of blades were varied to minimize total pressure distortion by restructuring the development of secondary flow. The results show that by using a properly designed vortex generator array total pressure distortion can be greatly reduced and flow separation can be totally prevented, the vortex generator with 8 pairs of blades reduced the circumferential distortion from 0.11 to 0.09. These results should provide valuable guidance in designing vortex generator installations in the S-shaped inlet.