Abstract: The effects of biological agents 3BY4 and BQ9 on resistance to tomato yellow leaf curl virus disease and on yield-promoting by spray were studied. Greenhouse test showed that3BY4 and BQ9 provided significantly control efficacy, with rates of 58.19% and 52.77% respectively. The control efficacy of 3BY4 and BQ9 to tomato yellow leaf curl virus reached 47.03% and 42.76%, respectively, under field conditions in Ganyu. Furthermore, the effects of strains 3BY4 and BQ9 on the yield and quality of tomato in fields were investigated. The yields were increased by 21.32% and 26.13% after application of 3BY4 and BQ9 respectively and they could also improve the tomato quality by increasing the contents of Vitamin C, soluble sugar, soluble protein and decreasing the content of organic acid. The field test in Beijing suburban area resulted that the control efficacy after treatment with the agents to Oudun was over 44%, but 17%-30% to Zhongnong 105 and Moneymaker, showing breeds variability. Our results suggest that 3BY4 and BQ9 have good effect against tomato yellow leaf curl virus and on yield-promoting and will have a broad application prospect in the future.