China is a country with high incidence of gastric cancer, with about 400,000 cases occurring every year, and the diagnosis of gastric cancer is mostly in the middle and late stages, i.e. the early diagnosis rate of gastric cancer is low. Therefore, the key to improve the survival rate of gastric cancer patients is early diagnosis. Early examination techniques for gastric cancer are as follows: 1. Gastroscopy: the main examination technique, which can observe tumor shape, size and growth characteristics, and also biopsy tissues for pathological diagnosis, and can remove tumor; 2. Ultrasonic gastroscopy: for tumors that do not invade mucous membrane or external lumen, it can simultaneously display the whole picture of tumor inside and outside the lumen, and understand the size and depth of tumor.