By using all the available meteorological observation data, climatic characteristics of sustained fog between 1980 and 2006 in the Pearl River Estuary Region were analyzed. Meanwhile, the circulation characteristics and physical mechanism for sustained fog generation and dissipation were studied through analysing the typical cases. The major conclusions can be drawn as follows: (1) Sustained fog in the Pearl River Estuary Region usually appears from October to May next year, especially in spring; (2) The weather situation when sustained fog happens can be divided into 3 kinds: type A， on the e〖JP2〗ast of low pressure (or inverted trough)； type B， in the rear(or bottom) of high pressure； and type C， in uniform pressure fields; (3) When severe sustained fog happens, the transportation of wetwarm advection, the weak lift motion and convergence of vapor flux at the surface layer and the drywarm cap in the midlower troposphere are the favorable conditions for condensation of vapor and maintenance of temperature inversion, the intrusion of drycold advection accompanied by northerly wind is the main factor for the fog dissipation.