The process of preparation water-soluble yeast(1→3)-β-D-glucan with enzymolysis was studied in this paper.Single-factor test and orthogonal test were conducted to study the influences of various factors on the yield of soluble polysaccharide.The optimal reaction conditions:enzyme concentration 0.15 U/mL,substrate concentration 0.5 g/100mL,reaction temperature 40 ℃,pH 3.5 and reaction time 0.5 h.The yield of soluble polysaccharide by these conditions is 80.3%.In order to determine the triple helix structure and the molecular configuration of the samples,Congo Red test and FT-IR spectra were used.The soluble polysaccharide by enzymolysis can stimulate the immune system of mice.Not only can it extend the survival time of the mice which was challenged by E.coli,but also can enhance the survival of it.