Abstract: In this paper, several cases of continuous dense fog were analyzed from October 2016 to March 2017, using the HTG-3 microwave radiometer installed at Urumqi Airport. Results show that: 1) Microwave radiometer can monitor the variations of boundary layer air temperature and humidity in real time with high temporal resolutiom. 2) Integrated Water Vapor (IWV) can reflect the growth and decline of water vapor in the air, and the continuous dense fog is mostly a slow process of water vapor dissipation. The increase and fluctuation of Liquid Water Path (LWP) correspond to the generation and dissipation of dense fog. 3) In the cases of continuous dense fog, below the height of 500-1000 m, the air is nearly saturated, and the relative humidity is almost higher than 95%. 4) The establishment or enhancement of the ground temperature inversion is the key factor to the formation of continuous dense fog.