Abstract: The tomato variety ‘Fentailang’ was used as the test material, and the seedling stage（T1）,flowering stage（T2）,fruiting stage（T3） and seedling stage+flowering stage+fruiting stage（T4） were set up in greenhouse cultivation mode to apply the same dose of microbial inoculants.With no microbial inoculants（CK） as the control, the morphological indexes, yield and quality（soluble sugar, soluble protein, vitamin C,organic acid, nitrate）,related enzyme activity and gene expression of tomato plants were determined, in order to clarify the promotion of microbial agents on tomatoes and the best application period.The results showed that the microbial inoculants significantly promoted the plant height, stem diameter, leaf number and fruit yield of tomato.The content of soluble sugar, soluble protein and vitamin C increased, while the content of nitrate decreased.The activities of sucrose synthase（SS） and neutral invertase（NI） in leaves increased, and up-regulated gene expression of sucrose synthase（SS）,sucrose phosphate synthase（SPS）,neutral invertase（NI） and acid invertase（AI） in fruits increased.In conclusion, the application of microbial inoculants can promote the growth of tomatoes, increase the yield of fruits, and promote the sucrose metabolism of fruits, so as to improve the quality of fruits, especially in the seedling+flowering+fruiting stage（T4）.