A novel enclosed air-jet electrospun set-up was described for fabricating nanofibers with high production rate. This study showed the components of the spinneret device, mainly including a spray nozzle, a liquid storage chamber, a connector and a gas storage chamber. By using this device, the polyacrylonitrile (PAN) nanofiber mats were fabricated with increased production rate of nearly more than ten times as compared with using single-needle electrospun set-up. The jets path, fibers morphology, mats throughput, along with forces acted on the bubbles in four positive electrodes were investigated in this report. The electric fields and equipotent lines distribution with corresponding positive electrodes were simulated with a second-dimension FEA (An-soft Maxwell) for analyzing experiment results. The simulated results showed that the strength of electric fields was related to the size of the charged area, and the uniform of electric fields depended on the mutual effects of electric fields from different charged position. The average diameter of fibers was the thinnest with about 280 nm and the standard deviation of fibers was 34.95 % with the top surface of the solution storage chamber and the nozzle charged. When the whole nozzle was charged, the diameter of fibers increased to 323.27 nm but the standard deviation reduced to 29.53 %. Especially, with the top surface of the solution storage chamber charged, the fibers showed thinner mean diameter of 290 nm and the most uniform standard deviation of 28.02 %. With further reduction of the charged area, a few beads-like fibers with the thickest diameter and the worst standard deviation were appeared.