The invention relates to a gastric cancer detection marker, and a detecting method thereof, a related kit and a biochip. The gastric cancer detection marker comprises 21 specific micro RNAs stable in human serum / plasma. The marker which is broad in detection spectrum, high in sensitivity, low in detection cost, easy to be got and stored can be used for diagnosing and differentially diagnosing the gastric cancer, predicating occurrence and reoccurrence of diseases and conditions, evaluating therapeutic efficiency and efficacy and screening active pharmaceutical ingredients and the like. The method can be widely applied to cancer survey and related work, improves low specificity and low sensitivity caused by individual difference which is difficult for a single marker to overcome, and remarkably improves the clinical detection rate of the gastric cancer. Therefore, the method is an effective means to diagnose early breast cancer.