The invention discloses a method for regulating the molecular weight of schizophyllan as a fermentation product of schizophyllum commune franch. The method comprises the following steps: taking slopestrains of schizophyllum commune franch, and carrying out slope inoculation and culture by adopting a PDA culture medium test tube, thereby preparing fermentation seed liquid; inoculating the seed culture liquid into a fermentation tank for fermentation, wherein the initial stage of fermentation is 0-36 hours, and the fermentation conditions are controlled as follows: the stirring rotation speed is 100-400r / min, the ventilation volume is 0.20-0.8vvm, and the temperature is 26-28 DEG C; the middle stage of fermentation is 37-84 hours, and the later stage of fermentation is 85-96 hours; and respectively controlling the fermentation conditions, discharging after the fermentation is ended, and removing mycelia; concentrating, precipitating, filtering to obtain refined schizophyllan. Accordingto the method disclosed by the invention, polysaccharides are degraded by utilizing enzyme self-secreted by the thalli, so that not only is the procedure of degrading after separating and purifying crude polysaccharides with larger molecular weight and poorer solubility and obtained by fermentation in the traditional method greatly simplified, but also the product yield is increased and the production cost is reduced.