The invention discloses a biological preservative and a preparation method thereof. The biological preservative is prepared from, by weight, 20-40 parts of nisin, 2-8 parts of trhalose, 5-10 parts of chitosan, 10-20 parts of compound amino acid, 4-8 parts of garlic, 10-15 parts of fresh ginger, 2-6 parts of pepper, 1-5 parts of clove, 2-8 parts of cinnamon, 2-6 parts of nutmeg, 2-5 parts of anise and 3-8 parts of fennel. According to the biological preservative, the components are subjected to compatibility, the synergistic effect is achieved, complementation and synergism are achieved, the bacteriostasis range can be enlarged, the preservative effect is enhanced, and the good antibacterial effect is achieved for bacteria, molds and yeast; meanwhile, garlic, fresh ginger, pepper, clove, cinnamon, nutmeg, anise and fennel contain a large number of natural active materials, the biological activity is achieved, amino acids are added jointly, the good health care functions such as appetite promotion and digestion aiding are achieved for body health, and the good popularization and application value is achieved.