The invention discloses a preparation method of a lentinan component with immunocompetence, which comprises the following steps: (1) coarsely crushing dried lentinan, and carrying out superfine crushing; (2) extracting the product in the step (1) with hot water, and collecting lentinan aqueous extract; (3) treating the lentinan aqueous extract with a micro-filtration membrane assembly with the pore diameter of 50-100 nm for solid-liquid separation, or filtering the lentinan aqueous extract with a PPS filter bag to remove insoluble substances and a lentinan extract B in the lentinan aqueous extract; and (4) performing ultrafiltration treatment on the lentinan extracting solution B in the step (3) with three ultrafiltration membrane assemblies. According to the invention, a multi-stage crushing and multi-stage filtering mode is adopted; effective separation of lentinan components is realized; meanwhile, convenience is provided for recovering trehalose and mannitol which are rich in smallmolecular components; the technical scheme is simple and easy to operate, large-scale preparation and production are easy to realize, the production process is green and safe, and the lentinan component obtained by the technical scheme contains less than or equal to 1% of protein, less than or equal to 3.2% of flavone and less than or equal to 2.8% of reducing sugar.