In order to improve the antibacterial property of silk fabric, nano-silver was used to deal with the silk fabric by steaming in the light of in-situ methanism. All of the factors which affect the content of nanosilver and the whiteness of the finished silk were studied. These factors are the concentration of RSD solution, the concentration of silver nitrate solution, the steaming temperature and the dipping time. The optimum technology obtained was showed as follows: the silk fabric should be treated with the concentration of 2g/L RSD and the concentration of 0.085g/L silver nitrate, and steamed for 30 minutes after dipped for 5 minutes. The results of the inhibition zone test and the antibacterial rate test indicated that both the silk fabric finished by the optimum technology and the one settled by five times diluted optimum technology showed highly antibacterial property. Even if the solutions are diluted by 5 times, the antibacterial rate of finished fabric is up to 99.67% to Staphylococcus aureus and 99.99% to Escherichia coli. Meanwhile, the inhibition zone is 7.9mm to Staphylococcus aureus and 8.3mm to Escherichia coli. In addition, the whiteness of the finished fabric was changed a little.