Abstract: Objective To study the effect of external irradiation on intestinal flora in patients with cervical cancer. 
Methods Fecal samples of 72 patients with cervical cancer before and after external irradiation radiotherapy were collected. The changes of intestinal flora were analyzed by Illumina NovaSeq high-throughput sequencing plat form. Patients were divided into pre-treatment group (T0 group) and post-treatment group (T1 group) by self-control method.And then patients were divided into non-radiation enteritis group (E0 group) and radiation enteritis group (E1 group) according to the degree of radiation enteritis. According to the tumor regression rate, the patients were divided into effective group (R1 group) and ineffective group (R0 group). Then, data of the changes of intestinal flora were analyzed. 
Results There was no significant difference in α diversity index in intestinal flora between T0 group and T1 group (P＞0.05). There was no significant difference in α diversity index and β diversity index before and after treatment between E0 and E1 groups (P＞0.05). In terms of microflora composition, it was found that Actinomycetales. Micrococaceae, and Rothia in E0 group, Lactobacillaceae, Bacteroidetes, Bacteroidales S24_7 and Bulleidia in E1 group increased after external irradiation. There was no significant difference in α diversity index and β diversity index between R0 and R1 groups (P＞0.05). However, the relative abundance of Bacteroides, f-Lachnospiraceae.g- Lactonifator, Pasteurella and Erysipelotrichaceae increased in R1 group. 
Conclusion There are significant changes in the structure and composition of intestinal flora in patients with cervical cancer before and after external irradiation, which may be related to the increase of radiation enteritis and may affect the short-term therapeutic effect. 

Key words: uterine cervical neoplasms, radiotherapy, gastrointestinal microbiome