Early diagnosis have great positive effect on the treatment of gastric cancer patients. Raman spectroscopy can provide a useful monitor for hemoglobin dynamics. Besides, Raman spectroscopy has notable advantages in the fields of abnormal hemoglobin diagnosis, hemoglobin oxygen saturation deter mination and blood methemoglobin analysis. In this paper, novel silver colloid was synthesized by microwave heated method. The surface enhanced Raman spectrums of hemoglobin from 11 normal persons and 20 gastric cancer patients are measured and analyzed in order to obtain spectrums which are high repeatability and characteristic peaks protruding. By analyzing the assignations of the SERS bands, it found that the content of asparagine, tyrosine and phenylalanine in the hemoglobin are significantly lower than healthy people. Discussing the structure of hemoglobin, when hemoglobin combines with oxygen, Fe2+is in a low spin state, ionic radius shrinks and moves 0.075 nm and fall into the pore in the middle of the heme porphyrin ring plane. This spatial variation affects F8His connected with the iron, will narrow the gap between the globin in the two strands of the helix, as a result, HC2 tyrosine pushed out of the void. Using this mechanism, the absorption peak of 1 560 cm-1 confirmed that the tyrosine content in patients with gastric cancer was lower than that of normal people. Principal component analysis(PCA) is employed to get a three-dimensional scatter plot of PC scores for the health and cancer groups, and it can be learned that they are distributed in separate areas. By using the method of discri minate analysis, it is found that the diagnostic algorithm separates the two groups with sensitivity of 90.0% and diagnostic specificity of 90.9%, the overall diagnostic accuracy was 90.3%.The results from this exploratory study demonstrate that, SERS detection of oxyhemoglobin combined with multivariate analysis would be an effective method for early diagnosis of gastric cancer.