The invention provides an application of a drug composition in the preparation of drugs for preventing salmonella infection in laying hens, improving egg laying performance of the laying hens, reducing the amount of salmonella in shells and contents of eggs and improving quality of the eggs of the laying hens. The drug composition comprises, by weight, 20-50 parts of gallnut tannic acid and 10-30parts of glycine. The drug composition has the advantages of green safety and no tolerance by taking 'source conditioning' as the core; replacing antibiotics, the drug composition can effectively inhibit and kill salmonella, eliminate endotoxemia caused by bacterial death and release of endotoxin, adjust the body's immune defense, purify salmonella from the laying hens, reduce horizontal spread ofsalmonella and egg-borne contamination caused by potential endogenous displacement of chickens, improve egg laying performance and the quality of the eggs and effectively avoid food safety problems caused by the egg-derived salmonella.