Esophageal cancer accounts for more than half of the world, seriously affecting people's health in China. 95% patients are squamous cell carcinoma. Surgery is the preferred treatment for early and middle stage esophageal cancer, but patients with clinical stage T4b or other surgical contraindications have no surgical opportunity. In recent years, radical chemoradiotherapy has played a key role in the treatment of local advanced esophageal cancer with some poor predicting biomarkers. Oral bacteria may play a pathogenic role in cancer and other chronic diseases by producing chemical carcinogens and inflammatory factors through direct metabolism. A large number of studies have also suggested that tooth loss and poor oral hygiene are closely related to upper digestive tract cancer, indicating the possible role of oral microorganisms in the occurrence and development of upper digestive tract cancer, and saliva is the main source of oral flora colonization. Therefore, it is worth further research to explore the interaction between microbial metabolism imbalance and radiotherapy in patients with esophageal cancer. In summary, we intend to conduct a prospective cohort study to explore the role of salivary microbes in radiotherapy in patients with initially inoperable patients with local advanced esophageal cancer.