Nonwoven microstructural geometries strongly influence the performance of nonwovens in practical application. Designing nonwovens for the specific environment of the targeted application will have to rely on the ability to understand microstructure of the media and model the nonwoven geometry. In recent years, hierarchically-structured fibers have received an increasing amount of attention. In this study, focusing on the micro-/nanofibrous nonwovens with helical fibers, which introduce enhanced properties, we develop a method to characterize nonwovens microstructure and to construct nonwoven geometry model. A co-electrospinning system is used to prepare nonwovens with helical nanofibers, and scanning electron microscopy is used to acquire the microstructural image. By developing a code called microstructural nonwoven analyzer (MiNA) based on digital imaging processing, fiber geometry in nonwovens, including fiber morphology and helix geometry, is successfully characterized. By combining MiNA and a developed model construction code, the nonwoven geometry model is constructed. This method provides the possibility in designing fibrous media with different fiber morphology.