A one-step synthesis procedure is developed to prepare flexible S0.6Se0.4@carbon nanofibers (CNFs) electrode by coheating S0.6Se0.4 powder with electrospun polyacrylonitrile nanofiber papers at 600 degrees C. The obtained S0.6Se0.4@CNFs film can be used as cathode material for high-performance Li-S batteries and room temperature (RT) Na-S batteries directly. The superior lithium/sodium storage performance derives from its rational structure design, such as the chemical bonding between Se and S, the chemical bonding between S0.6Se0.4 and CNFs matrix, and the 3D CNFs network. This easy one-step synthesis procedure provides a feasible route to prepare electrode materials for high-performance Li-S and RT Na-S batteries.