A kind of biomimetic fibers of helical structures at nanoscale has attracted increasing interest. In this study, a novel co-electrospinning setup with a designed flat spinneret, used for the fabrication of helical nanofibers, is reported in this study. Poly(m-phenylene isophthalamide) (Nomex) and Thermoplastic polyurethane (TPU) are chosen as the two components in co-electrospinning. To display the efficiency for producing helical fibers, a generally used core-shell needle spinneret is used for comparison. The effect of the uniformity of electric field distribution created by these two types of spinnerets on the jet motion and the resultant helical fibers is developed, with systematical simulation and experimental research. The results showed that the co-electrospinning system with the newly designed flat spinneret can produce helical nanofibers efficiently. Compared with the needle spinneret, the flat spinneret created more uniform electric field, leading to better morphology and structure of the resultant helical fibers. In addition, an approach to achieve the scale-up of this co-electrospinning system is developed. This novel design is expected to provide a promising method to fabricate nanofiber materials with helical structures. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019