In order to detect the effect of gold nanoparticles on gastric tumor tissue in near-infrared optical imaging, the spectral feature in near-infrared is observed after gold nanoparticles piled up in tumor tissues of gastric as a contrast agent. The MCG-803 human gastric cancer cell line (from CTCC) is subcutaneously inoculated in BALB/C nude mice, and then the orthotopic graft model of gastric cancer is made. Animals are divided into two groups: gastric tumor tissue control group and gastric tumor tissue with gold nanoparticles group. The optical attenuation coefficients of tumor tissue are detected by a near-infrared spectroscopy. The results show that the shape of the transmittance spectra of tumor tissues with gold nanoparticles and tumor tissues without gold nanoparticles is similar in near-infrared range from 800 to 1500 nm. But the spectral transmittance is slightly lower than that of the corresponding tumor tissue about 4.4% to 7.0%. And there are significant differences at the statistical sites of 900, 1000, 1100, 1200, 1300 and 1400 nm. The present study has suggested that gold nanoparticles accumulated in nude mice gastric cancer can affect on optical properties tumor of tissue, which can provide a theoretical guidance for the optical imaging detection of tumor tissue.