Objective To explore the clinical value of transabdominal gastric ultrasonography in the diagnosis of gastric cancer. Methods The data of 129 gastric cancer patients diagnosed and treated in Chongming Branch of Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Kongjiang Hospital of Yangpu District, and Jiading Central Hospital of Shanghai University of Medicine & Health Science from Jan. 2010 to May 2020 were retrospectively analyzed. All patients were diagnosed with gastric lesions on the first examination of transabdominal gastric ultrasonography, then underwent gastroscopy, and were finally pathologically proven with gastric cancer by gastric mucosal biopsy. McNemar method was used to compare the detection rates of suggestive lesions, the overall qualitative diagnosis accuracy and the qualitative diagnosis accuracy of different gastric parts between gastroscopy and ultrasonography. Results Advanced gastric cancer accounted for 93.0% (120/129) and early gastric cancer accounted for 7.0% (9/129). With the histopathological diagnosis as the gold standard, no false positive cases were detected by transabdominal gastric ultrasonography, and the detection rate was 100.0% (129/129); 128 cases of gastric lesions were detected by gastroscopy, and the detection rate was 99.2% (128/129). For the one misdiagnosed case by gastroscopy, ultrasonography showed significant thickening of gastric antrum wall, while gastroscopy showed hyperemia, edema and coarse folds of gastric mucosa without other obvious abnormalities, but it was confirmed as poorly differentiated adenocarcinoma by postoperative pathology. The sonographic features of gastric cancers showed that thickened, excavated and protruded lesions accounted for 46.5% (60/129), 41.1% (53/129) and 12.4% (16/129), respectively. The maximum thickness and diameter of the lesions were (13.5±5.1) mm and (56.8±24.9) mm, respectively. The diagnostic accuracy of ultrasonography and gastroscopy for gastric cancer was 74.4% (96/129) and 82.2% (106/129), respectively, showing no significant difference (P>0.05). There was no significant difference in the diagnostic accuracy for cancers in the gastric antrum, gastric body, gastric angle, gastric fundus, cardia or gastric stump between ultrasound and gastroscopy (all P>0.05). Conclusion Transabdominal gastric ultrasonography has a good ability to detect gastric wall lesions, and its application can further improve the detection rate and diagnostic accuracy of gastric cancer.