Abstract: Based on spectral profiles sampling from EOS MODIS data, the spectral characteristics of water, cloud, snow, surface features and fog are analyzed; Channels suitable for fog detection are discovered. On the basis of this, the advection fog, which occurred at 13:21 on Jan.5, 2004 and at 01:27 on Jan.6, 2004, in Liaoning Province and Liaodong Gulf, is detected. Validated from ground truth data, the result shows that MODIS data has great potential in fog detection.