The invention provides a collagen gel and a preparation method thereof. The collagen gel comprises collagen and an antibacterial agent, wherein the antibacterial agent is at least one of chitosan and nano silver. The collagen gel also comprises a preservative, a substrate, a dispersing agent, a film-forming agent and water; and 1g of gel comprises 0.5 to 8.0mg of collagen, 0.001 to 15mg of antibacterial agent, 1 to 50mg of preservative, 10 to 50mg of matrix, 50 to 100mg of dispersing agent, 1 to 10mg of film-forming agent, and the balance of water. The method for preparing the collagen gel comprises the following steps of: performing dispersion and dissolution on the substrate by adopting the dispersing agent under ten-thousand grade clean environment; adding the dispersing agent, the substrate, the preservative, the antibacterial agent, and collagen solution into a vacuum emulsified homogenizer one by one; after fully mixing, standing and defoaming, filling the product. The collagen gel is applied to various open wounds and infected wounds, lightens hyperpigmentation, has good effect of accelerating wound healing, and can maintain long-term anti-bacteria function.