Three fog events in Beijing were dynamically monitored in real time from the end of October to early December in 2011 using the visibility and relative humidity data from surface AWS (Automated Weather Station) and artificial observation, comparing with fog thickness data detected by satellites. The results show that the processes of fog occurrence, development, and dissipation can be monitored by means of the visibility and relative humidity observation. Comparing with the analysis of satellite data，the visibility and relative humidity data have the same trend and advantages in detecting the life cycle of a fog event.