The invention provides a composite protective agent for increasing the freeze-drying survival rate of lactobacillus plantarum and a preparation method thereof. The protective agent is prepared from soybean polysaccharide, galactose, fructo-oligosaccharide, trehalose, skimmed milk, proline and distilled water. The preparation method includes the steps that the distilled water is divided into three parts, and soybean polysaccharide, galactose, fructo-oligosaccharide and trehalose are added to one part for dissolution and sterilization; the skimmed milk is added to another part of the distilled water for dissolution, and a skimmed milk solution is obtained and sterilized; proline is dissolved in the remaining distilled water, and membrane filtration sterilization is conducted; the three prepared solutions are evenly mixed under the sterile condition, and then the composite freeze-drying protective agent is obtained. According to the freeze-drying protective agent for lactobacillus plantarum, a freeze-drying protective additive is added in the fungus powder preparation process, the anti-freezing capacity of fungi can be improved, and therefore the freeze-drying survival rate of the fungus powder is increased, the storage period is long, and the survival rate is not likely to be reduced. The freeze-drying survival rate of the prepared fungus powder of lactobacillus plantarum ranges from 82.73% to 93.26%, and the viable count of the fungus powder ranges from 1.14*10<11> cfu/g to 1.98*10<11> cfu/g.