Aramid fibers exhibit outstanding properties such as heat resistance, chemical resistance, dimensional stability, durability and elongation. However, their poor dispersibility poses a significant challenge when preparing composites. Consequently, converting aramid fibers into nanofibers is crucial to enhance their dispersibility. In this study, aramid nanofibers with excellent dispersibility were prepared by applying a supercritical fluid drying process. Technora based copolymer para-aramid nanofibers (CANF) were prepared by reacting in a DMSO/KOH basic solution within a short processing time (i.e., less than 3 h), and dried by a supercritical fluid process. We obtained uniformly dispersed CANF without the change in chemical composition. In addition, uniform translucent membrane sheets were prepared by vacuum filtration methods. Their tensile strength was obtained to be 23 MPa with high dimensional stability even at 100 °C without shrinkage, which can provide the possibility of CANF sheets as a separator for lithium-ion batteries.