The invention belongs to the technical field of marine organism applications, and relates to a preparation method for extracting phycoerythrobilin, polysaccharides and dietary fibers from low valued lavers and an application of the preparation method. According to the method, after the low valued lavers are dewatered, chopped and soaked in entrainers, by the aid of a supercritical CO2 fluid extraction technology, extraction, separation and purification are performed at proper packing liquid-solid ratio, extraction temperature and extraction pressure to obtain the phycoerythrobilin and the laver polysaccharides. Fishy smell removing agents are added into residual algal residues to remove fishy smell, and the residual algal residues are dried, activated and granulated to obtain the laver dietary fibers. The preparation process is simple, stable, green and efficient, and the obtained three products are fine in powder, high in purity and free from algal fishy smell, and can serve as various food raw materials.