The present invention relates to a homogeneous polysaccharide with an immunoregulation activity and a preparation method thereof. The homogeneous polysaccharide with the immunoregulation activity is a single chromatographic peak and has a molecular weight of 6880±50 Da and an optical rotation value of 158.4±0.5°. An infrared spectrum has an α-configuration sugar characteristic absorption peak at 847.6 cm−1. Hydrogen-proton characteristic chemical shifts in hydrogen spectra of the polysaccharide are δ 5.40, 3.95, 3.84 and 3.61. Carbon signal characteristic chemical shifts in carbon spectra are δ 99.6, 76.6, 73.3, 71.5, 71.1 and 60.4. The homogeneous polysaccharide has an effect of enhancing body immunity, can achieve excellent anti-tumor, antiviral and anti-infection effects and the like in regulation of immunity-related diseases, and has potential development values in drug and health care product industries for treatment and prevention of the diseases.