This work presents a new way of preparing bead-free and core-shell superfine polymer electrospinning fibers under the assistance of another polymer and an interfacial compatibilizer. For the electrospinning of polystyrene (PS)/CHCl3 solution, the bead-free fiber cannot be obtained until the PS concentration is above 0.25 g/mL but its average diameter is above 10 mu m. Using polyamide 6 (PA6) as an additive, the critical concentration capable of forming bead-free fiber greatly decreased and core-shell fibers with PA6 as the core and PS as the shell were obtained due to the driving effect of high spinability of PA6. The introduction of a copolymer (PS-co-TMI) of styrene (St) and 3-isopropenyl-alpha,alpha-dimethylbenzene isocyanate (TMI) can react with amine of PA6 to form the copolymer of PS and PA6 as an interfacial compatibilizer. As a result, it can further enhance the dispersion and deformation of minor component PA6 into uniform microfiber core, and drive PS to uniformly cover the surface of PA6 fibers, and finally form bead-free and core-shell superfine fibers. POLYM. ENG. SCI., 59:1437-1444 2019. (c) 2019 Society of Plastics Engineers