Abstract: With intensive surface observations for the area of Pearl River Delta, a local meso-and-small-scale weather system,cold air surge from the rear of the front,is identified and analysed in detail for determination of its surface structure and effects on weather. The result shows that the convective system acts in a manner very close to tropical squall lines by bringing explosive hard rain in assication with weak tendency for strong winds for the area of interest. It covers 30-60 km horizontally and lasts up to 4 hours, moving at 60 km/h in constant direction. It would be enhanced or weakened as it migrates into or out of the area. It is the strong isallobric area excited by the front edge of cold mesohigh that directly causes the surface divergent outflow, squall front and assciated convective weather, a contrast against classic squall struture.The isallobaric area weakens and the convective system disaipates as a result as they gradually separate from each other in motion.