Longmen Grottoes is one of key cultural relic units under the state-level protection, which were carved in the carbonate rocks, and Fengxian Temple is one of the representative works of Longmen Grottoes. In this paper, the seepage of Fengxian Temple had been detected under different conditions by means of infrared thermal imaging. And the results show that using thermal imaging devices can detect the seepage of the cliff rock site accurately and effectively, and what’s more, the source of water seepage, the distribution and activity patterns of the seepage can be determined too. Compared with previous human observation, infrared thermal imaging has obvious advantages.