Based on visibility and fog data from 1980 to 2000, the characters of fog and visibility, and the evolvement rules are studied. The result shows that visibility in summer is better than that in Winter. This may be caused by different prevailing wind, transportation of pollutants, and different weather condition between winter and summer. There is a downtrend of Xiamen's visibility. Days of light fog are increasing. Visibility in Xiamen is much better than that in Beijing where is serious pollution. Xiamen's visibility has distinctly daily variations, it is related with sea land breeze in summer.