The application of hydroponic technology in vegetable production is an important supplement to the traditional soil cultivation mode and an important means of modern agriculture，so it is important to study the composition and function of microbial community in the root of hydroponic lettuce by using different proportion of nitrogen sources.The hydroponic test site was located in Wenjiang district，Chengdu city，Sichuan province.The nutrient solution treatment included:100% inorganic nitrogen(T1)，100% organic nitrogen(T2)，50% inorganic nitrogen and 50% organic nitrogen(T3)，with all treatments set up with replications.The control of the growth process of lettuce in three treatments was the same，except the nitrogen addition was different in the nutrient solution of hydroponics.A high throughput sequencing method was used to determine the microbial community structure in the root of lettuce and to predict its function.Diversity analysis showed that there was no significant difference in bacterial species among the three treatments，but the highest bacterial richness and evenness was observed in the root of lettuce treated with 100% organic nitrogen.The results of principal coordinate analysis showed that the community structure of root bacteria under T2 treatment was quite different from that of T1 and T3 treatment，and that of T1 and T3 treatments was relatively similar.Species composition analysis showed that，at the order level，the 10 most abundant taxa were pseudomonadales，sphingomonas，xanthomonas，Betaproteobacteria，stipe，rhizobium，flavobacterium，steroid baciliales，Salinisphaerales and Rickettsiales.Pseudomonadales was the dominant group in TI and T3 treatments，Xanthomonadales was the second dominant group in T1 treatment.Sphingomonadales was the dominant group in the T2 treatment.Ten distinct species were found at genus level，among which Sphingobium，Asticcacaulis，Pelomonas，Phenylobacterium，uliginosibaterium，IS-44，Methylopila and Pseudolabrys had the highest Indval values among the root bacteria of lettuce under T2 treatment，the Indval values of Stenotrophomonas and Aeromonas were the highest in the T1 treatment and the Indval value of Chryseobacterium was the highest in the T3 treatment.Functional prediction analysis of PICRUSt2 showed that carbohydrate metabolism and amino acid metabolism were the most abundant metabolic pathways in the three treatments，and the metabolic activities of amino acid metabolism，cofactors and vitamins were significantly increased under T2 treatment，and the difference with T1 and T3 treaments was significant or extremely significant，however，lipid metabolism，terpenoids and polyketones metabolism，signal transduction，cell movement，endocrine system biosynthesis，glycan metabolism and infectious disease activity were significantly lower than those of T1 and T3 treatments.Adding organic nitrogen nutrient solution to lettuce root had higher bacterial abundance and stronger functional characteristics.However，if only 50% organic nitrogen nutrient solution was added，the effect on bacterial community and function was not obvious.The formula of 100% organic nitrogen source nutrient solution may bring more positive effects on the growth and quality of lettuce.