Abstract: Offshore gale over the Bohai and the Yellow Sea was caused by frontal passage on Feb. 13, 2009. WRF Model was employed to simulate the gale to investigate the mechanism and distributional characteristics of physical factors. Evolution and intensity of weather systems in upper-level, middle-level and lower-level for this frontal gale were well simulated by the model, which successfully reproduced the main traits of circulations and controlling synoptic system over the Bohai and the Yellow Sea. The gale was mainly caused by cold front of wind cooling process, with invading cold air and growing surface pressure gradient force, during which wind speed increased as well. This was a reflection of the warm and cold air baroclinicity and wind speed enhanced by the surface baroclinicity. Simulation of physical factors indicated that surface wind speed could increase when upward motion turns to downward motion over observation station and the speed was proportional to the intensity of downward motion. Temperature and relative humidity distribution was a reflection of weather systems development when cold front passed by.