Co-electrospinning is a new branch of nanotechnology for producing composite nanofibers with collective functions and special fiber structures. Helical fibers in nanoscale have been of increasing interest because of their unique characteristics. In this work, we report the fabrication of the helical nanofibers with polyurethane and poly(m-phenylene isophthalamide) by the co-electrospinning system with an off-centered coreshell spinneret. High-speed photography and three-dimensional (3D) electric field simulation are carried out to help in understanding the formation of the helical structures. The asymmetrical electric field distribution may be a factor affecting helical fiber formation. We also show that a series of factors such as the applied voltage, the conductivity of the system, and the composite ratio have considerable effects on the morphologies of the produced helical nanofibers. This work can provide a promising technique for producing nanofibrous nonwovens with helical fiber morphology.