A fiber pre-dispersing device for fiber reinforced concrete, comprising: a dispersing chamber, a feed inlet is installed on the upper side of a dispersing chamber, a hopper is installed in the feed inlet, a first dispersing device is installed in the dispersing chamber, a discharge outlet is installed at the bottom of the dispersing chamber, and connected with a second dispersing device, grooves are arranged at both sides of dispersing chamber, supporting legs are installed in the grooves. According to the invention, the device has a first dispersing device and a second dispersing device, and the dispersing blocks in the first dispersing device cooperates with the dispersing gears of the roller to preliminarily disperse and stir the fiber raw materials, a second dispersing device; dispersing the preliminary dispersed fiber raw materials, in order to control the fineness of pre-dispersed fiber raw materials, oil cylinders arranged on both sides can push their respective grinding cylinders to adjust the dispersion, thus improving both fiber dispersion effect and using the effect in concrete works.