The invention discloses a food fresh keeping agent. The food fresh keeping agent is prepared from two raw materials of sowthistle tasselflower herb and sodium alginate. A sowthistle tasselflower herbextract contains a plurality of flavonoids and alkaloids, has high restraining effect on harmful bacteria of staphylococcus aureus, pseudomonas aeruginosa and the like, and can cooperate with sodium alginate for use, so that the air can be effectively separated; and the sodium alginate also has favorable bacterial inhibition properties, and is good in sterilization effect. The food fresh keeping agent is simple to operate, the raw materials are broad in sources, the cost is low, and the food fresh keeping agent is easy to popularize.