The present invention discloses Penicillium oxalicum EU2101 and applications of the Penicillium oxalicum EU2101 in preparation of a cellulase preparation and degradation of cellulose, wherein the Penicillium oxalicum EU2101 has the preservation number of CGMCC No.12769. The invention further provides a cellulase preparation prepared by using the Penicillium oxalicum EU2101, wherein the preparation method comprises: culturing the Penicillium oxalicum EU2101 at a temperature of 28-42 DEG C by using a culture medium, and collecting the fermentation product to obtain the cellulase preparation. According to the present invention, the experiment results prove that after the Penicillium oxalicum EU2101 is subjected to solid state fermentation culture, the extraction liquid has cellulase activities such as filter paper enzyme activity, CMC enzyme activity, Avicel enzyme activity, pNPC enzyme activity and pNPG enzyme activity, and can effectively hydrolyze the manihot esculenta residue being subjected to an alkali pretreatment to produce glucose, such that the application potential is provided in conversion and utilization of the manihot esculenta residue.