A method for extracting water soluble beta-glucan from inonotus obliquus sporophore comprises the following steps: 1, inonotus obliquus crude polysaccharide preparation, to be more specific, taking inonotus obliquus sporophore, crushing to obtain powder, extracting the powder with lye, filtering to remove a residue, adding ethanol into filtrate, standing, filtering to obtain a precipitate to obtain inonotus obliquus crude polysaccharide; 2, inonotus obliquus beta-glucan preparation, to be more specific, taking the inonotus obliquus crude polysaccharide, drying, adding water, mixing, adding alpha-amylase for hydrolysis, filtering hydrolysate, removing filtrate to obtain a residue to obtain inonotus obliquus beta-glucan; and 3, water soluble beta-glucan preparation, to be more specific, taking the inonotus obliquus beta-glucan, adding lye for stirring and extraction, adjusting pH of the extracting solution to 2.0-6.8, heating for hydrolysis, filtering hydrolysate, adding ethanol into filtrate, standing, separating a precipitate and drying to obtain the soluble beta-glucan. According to the method, the yield of inonotus obliquus polysaccharide is improved, water solubility is increased, and the water soluble beta-glucan is more conducive to body absorption.