In order to study Fe₃O₄-Polypyrrole (Fe₃O₄-PPy) core-shell nanocomposite in the diagnosis of tumor markers in the diseased gastric tissues of early cancer patients, a total of 160 cases of patients, who were confirmed as early gastric cancer by gastroscopy or postoperative pathology at a designated hospital of the study from December 2014 to December 2018, were selected as research objects and were divided into two groups of observation and control group with 80 cases in each group. For each patient in the two groups, two pieces of diseased gastric tissue were firstly taken through gastroscopy; then the observation group applied Fe₃O₄-PPy with the particle diameter of 150-350 nm as carrier to detect the contents of carbohydrate antigen 19-9 (CA19-9), alpha-fetoprotein (AFP), carbohydrate antigen 242 (CA242), carcinoembryonic antigen (CEA) and carbohydrate antigen 72-4 (CA72-4) in the diseased gastric tissue, while the control group directly detected the contents of corresponding tumor markers; after the detections, the sensitivity, specificity and diagnostic efficiency of each marker in the two groups of patients were calculated, and receiver operating characteristics (ROC) curves with the areas under the curves (AUC) were drawn to analyze the correlation between the level of Fe₃O₄-PPy and the detection efficiency of gastric cancer markers. The results show that the detection sensitivity (82.17%, 80.32%, 79.48%, 84.63%, and 85.66%) and specificity (76.75%, 79.66%, 81.07%, 83.47%, and 85.24%) of CA19-9, AFP, CA242, CEA, and CA72-4 in the tumor tissue of patients in observation group for the diagnosis of early gastric cancer are higherthan the sensitivity (78.66%, 79.25%, 76.18%, 82.11%, and 83.45%) and specificity (74.37%, 76.94%, 77.24%, 81.22%, and 81.59%) of that in control group with statistically significant differences (P < 0.05). Therefore, it is believed that the Fe₃O₄-PPy is of great significance for the detection of early gastric tumor markers in the tissues of patients with early gastric cancer, and has certain value for the auxiliary diagnosis of early gastric cancer and the observation of therapeutic effects. This study results provide a reference for the further researches of Fe₃O₄-PPy in the diagnosis of tumor markers in patients with early gastric cancer.