The invention discloses a method for using subcritical water to extract grifolan. The method comprise the steps of stoving, smashing, subcritical extraction, rough filtration, heat preservation, centrifugation, concentration, purification, decolorization, precipitation, drying, re-washing, drying, secondary extraction and the like. The method specifically comprises the steps of taking advantages of good permeability and solubility of the subcritical water to make cell wall polysaccharide be in full contact with the subcritical water so that the cell wall polysaccharide can be fully dissolved out, conducting concentration on the cell wall polysaccharide through a water bath method, conducting purification on the grifolan by combining an Sevag method, and at the same time recycling a first centrifugation precipitation which can be used for conducting the secondary extraction on the grifolan. In this way, not only extraction content of the grifolan is increased, waste in raw material is also sharply reduced. Compared with existing other extraction methods, both the equipment cost and the operation cost according to the method for using the subcritical water to extract the grifolan are relatively lower, and extraction efficiency and purity of the grifolan are obviously improved.