【Objective】 To analyze the association between the composition of gut microbiota and blood pressure in children aged 6 - 9 years, in order to provide new ideas for childhood hypertension prevention and treatment. 【Methods】 A total of 411 children aged 6 - 9 years were recruited in Guangzhou from December 2015 to March 2017. The gut microbiota was characterized by 16S ribosomal RNA amplicon sequencing. The multivariate methods with unbiased variable selection in R (MUVR) were performed to identify the significant OTUs. Spearman correlation as well as multiple linear regression were used to explore the relationship between gut microbiota and blood pressure in children. 【Results】 Significant difference in β diversity index was observed between children with normal blood pressure and those with abnormal blood pressure (R²weighted=0.015,Pweighted=0.01; R²unweighted=0.027, Punweighted=0.001). After adjustment for covariates and controlling the false discovery rate (FDR), multiple linear regression analysis showed that blood pressure level in children decreased with the increasing abundance of OTU_3 (genus Blautia), OTU_131 (genus [Clostridium]_innocuum_group), OTU_1776 (genus Blautia), OTU_2159 (genus Prevotella) and OTU_91 (species Bifidobacterium_breve) (β:-0.18 --0.14; PFDR<0.05. In contrast, blood pressure in children increased with the increasing abundance of OTU_108(genus Sutterella), OTU_1(species Faecalibacterium_prausnitzii)、OTU_8(genus Roseburia), OTU_48 (genus Lachnoclostridium), OTU_81 (genus Coprococcus), OTU_401 (family Lachnospiraceae), OTU_1284 (family Lachnospiraceae) and OTU_2793 (family Lachnospiraceae)(β: 0.14 - 0.21; PFDR<0.05. The influence of gut microbiota on systolic pressure and diastolic pressure may be mediated by the increase of body mass index (BMI). 【Conclusions】 Pediatric blood pressure level is associated with the composition of gut microbiota, while BMI partially plays a mediating role in the relationship. It is recommended to modulate the abundance of microbiota as genus Blautia, Sutterella and so on to prevent hypertension in children.