Esophageal cancer is a common malignant tumor in China. Most of the esophageal cancers are squamous cell carcinoma, a few are adenocarcinoma, and some are carcinosarcoma and melanoma. Esophageal cancer generally passes through stages of epithelial atypical hyperplasia, carcinoma in situ and invasive carcinoma. Even if the surgery completely removes esophageal cancer, the long-term survival rate of many patients is low. Therefore, early detection, early diagnosis and early treatment are important for esophageal cancer, and some early detected esophageal cancer can be completely cured. However, esophageal cancer is insidious in its onset, how can it be detected early?