The invention provides a device for detecting polysaccharide in fermentation liquor based on Raman spectroscopy and a method and application thereof, and belongs to the technical field of fermentation liquor detection. The device for detecting the polysaccharide in the fermentation liquor based on the Raman spectrum comprises a fermentation tank, a reflector, an optical fiber probe, an optical fiber, an excitation light source, a detector, a signal acquisition module, an A/D conversion module, a single chip microcomputer and a display module, wherein the reflector is located in the fermentation tank, the excitation light source is connected with the optical fiber probe through an optical fiber, the optical fiber probe is connected with the detector through an optical fiber, the detector is further connected with the signal acquisition module, the signal acquisition module is connected with the A/D conversion module, the A/D conversion module is connected with the single-chip microcomputer, and the single-chip microcomputer is connected with the display module. Compared with the traditional polysaccharide detection method, the device provided by the invention does not need purification and separation, simplifies the detection steps, saves the detection time, reduces the polysaccharide detection cost, and has good practical application value.