Abstract: Studied the influence of voltage and distance from spinneret to collecting screen on microstructures of electro-spun silk fibroin fiber with regenerated silk fibroin(SF)-formic acid as the spinning solution at the concentration of 9%.The results showed that 9% is an ideal concentration of SF-formic acid solution which has good spinnability when the distance is constant(10 cm) with varied voltage or the voltage is constant(12 kV) with varied the distance.When the distance is 10 cm,there is a complex change in molecular conformation of the fiber with the increase of voltage,and the variation rule of crystallinity is also in discorder.When the voltage is 12 kV,the molecular weight of random/α-helical conformation in the fiber increases with the increase of the distance,but the crystallinity increased only slightly,then decreases sharply.