To provide a real-time intraoperative feedback and suggest an applied potential to guide stomach cancer surgery for removal of normal tissue as little as possible, we use an optical coherence tomography (OCT) to image normal tissue and tumor tissue of 39 stomach cancerous patients, and compare OCT images and pathological sections. The results show that OCT images of 38 patients show obvious difference between normal tissue and tumor tissue. For the 4 stomach mucinous carcinomas, the mucus secreted by tumor of stomach mucinous carcinoma destroys the layer structure, texture, and mucosa of stomach tissue. The poorer backscattering of mucus and the greater difference between backscattering of mucosal tissue make the OCT images of stomach mucinous carcinoma clearer. The B-mode ultrasonic scanning (B-scan) OCT images can distinguish the boundary of the cancerous tissue and the normal tissue. A volumetric image can be built with B-scan images by the three-dimensional (3D) reconstruction method. The layered section images in tissue-depth direction are obtained after volumetric surface flattening. These images provide another dimensionality to view stomach cancerous boundary. The cross validation with B-scan images can show excellent distinction.