The invention discloses a device and a method for converting sideband and random laser. The device comprises a laser, a box structure and a heating device connected with the box structure. Cholesteric liquid crystal mixed solution doped with laser dye is filled in the box structure. The method includes connecting a box filled with the cholesteric liquid crystal doped with the laser dye with the heating device; adjusting temperature of the cholesteric liquid crystal box when pumping light irradiates to the box structure and converting the sideband laser and random laser. The device and the method have the advantages of simplicity, easy implementing, low energy consumption and controllability in wavelength and line width of output laser.