Disclosed are the action and use of water extracts and polysaccharides from Fusarium oxysporum in immune enhancement, which belong to the field of biological medicine. The water extracts and polysaccharides from Fusarium oxysporum have a significant immune enhancement effect, which can promote the proliferation of macrophages, increase the phagocytic ability of macrophages, activate macrophages to release immunological active factors NO, IL-1α and TNF-α and can be used in lower immune function diseases and tumor adjuvant treatment.