The invention provides a random fiber laser system and belongs to the novel laser device field. In the system, a traditional single-mode fiber is taken as a laser medium, and a cascaded semiconductor laser is taken as pump light which is coupled to the fiber along an opposite direction from a middle point of the fiber. Photon is in propagation in the fiber, scattering is generated because of nonuniform random refractive index, and distributed Rayleigh scattering is formed. The pump light provides distributed Raman gain along the fiber. When total gain is greater than total loss, backward scattered photon is amplified to generate laser. Frequency of random laser is a result of frequency of last grade pump light shifting downward with 13 THz. By properly selecting pump light, output of the random laser in a whole fiber transparent window is realized. By using cascaded semiconductor laser as the pump light, not only is Raman gain spectrum bandwidth increased, but also Raman gain form is controlled. Thereby the random laser in the invention has the characteristics of controllable mode, super-long transmission, low threshold, high output power and the like.