Polyurethane (PU) nanofibers were fabricated by solution blowing. The effects of polymer concentration, gas pressure and temperature on morphology and diameter of fiber were discussed. The results show that the fiber with mean diameters in 100nm- 400nm range was successfully obtained, and when the mass fraction of the solution increases, the diameter of the fiber increases. On the whole, the evenness of the fiber diameter tends to decrease. The gas pressure and the temperature affect the fibers’ diameter, and as the gas pressure increase, the diameters of the fiber decrease, while the fiber diameter is gradually larger as the temperature increasing.