For sea fog events auto-monitor from satellites, the visible and infrared spectral radiance characteristics of sea fog, water surface, and cloud regions are analyzed based on data analysis from AVHRR3/NOAA17 observations. The remote-sensing optical radiance characteristis of sea fog are analyzed. It is found that there exists obvious spectral difference between sea fog and others. In sea fog region, the satellite-measured reflectance relation of channel 3a (1.58～1.64 μm), channel 1 (0.58～0.68 μm) and channel 2 (0.725～1.0 μm), is RCh1>RCh3a>RCh2 and even RCh3a>RCh1>RCh2, which are different from the RCh1>RCh2>RCh3a of ocean and some cloud bodies. With the Streamer radiative transfer model, the fog and clouds spectral properties of AVHRR3 Channel 1, 2 and 3a are simulated under different fog/cloud microphysical and observational conditions. The simulations are consistent with observations. The reflectance of Channel 3a is affected by the size of particle, that is, the smaller is the size, the higher reflectance is. Finally, those fog and cloud spectral properties are explained with Mie scattering theory.