Differential diagnosis for epithelial tissues of normal human gastric, undifferentiation gastric adenocarcinoma, gastric squamous cell carcinomas, and poorly differentiated gastric adenocarcinoma were studied using the Kubelka-Munk spectral function of the DNA and protein absorption bands at 260 and 280 nm in vitro. Diffuse reflectance spectra of tissue were measured using a spectrophotometer with an integrating sphere attachment. The results of measurement showed that for the spectral range from 250 to 650 nm, pathological changes of gastric epithelial tissues induced that there were significant differences in the averaged value of the Kubelka-Munk function f(ｒ∞) and logarithmic Kubelka-Munk function log［f(ｒ∞)］ of the DNA absorption bands at 260 nm between epithelial tissues of normal human stomach and human undifferentiation gastric cancer, between epithelial tissues of normal human stomach and human gastric squamous cell carcinomas, and between epithelial tissues of normal human stomach and human poorly differentiated cancer. Their differences were 68.5%(p＜0.05), 146.5%(p＜0.05), 282.4%(p＜0.05), 32.4%(p＜0.05), 56.0%(p＜0.05) and 83.0%(p＜0.05) respectively. And pathological changes of gastric epithelial tissues induced that there were significant differences in the averaged value of the Kubelka-Munk function f(ｒ∞) and logarithmic Kubelka-Munk function log［f(ｒ∞)］ of the protein absorption bands at 280 nm between epithelial tissues of normal human stomach and human undifferentiation gastric cancer, between epithelial tissues of normal human stomach and human gastric squamous cell carcinomas, and between epithelial tissues of normal human stomach and human poorly differentiated cancer. Their differences were 86.8%(p＜0.05), 262.9%(p＜0.05), 660.1%(p＜0.05) and 34%(p＜0.05), 72.2%(p＜0.05), 113.5%(p＜0.05) respectively. And pathological changes of gastric epithelial tissues induced that there were significant differences in the averaged value of the Kubelka-Munk function f(ｒ∞) and logarithmic Kubelka-Munk function log［f(ｒ∞)］ of the β-carotene absorption bands at 480 nm between epithelial tissues of normal human stomach and human undifferentiation gastric cancer, between epithelial tissues of normal human stomach and human gastric squamous cell carcinomas, and between epithelial tissues of normal human stomach and human poorly differentiated cancer. Their differences were 59.5%(p＜0.05), 73%(p＜0.05), 258.9%(p＜0.05), 118.7%(p＜0.05), 139.2%(p＜0.05), and 324.6%(p＜0.05) respectively. It is obvious that pathological changes of gastric epithelial tissues induced that there were significant changes in the contents of the DNA, protein and β-carotene of gastric epithelial tissues. The conclusion can be applied to rapid, low-cost and noninvasive the optical biopsy for gastric cancer and provides a useful reference.