A squall line with two different gust fronts occurred in central Liaoning in August 2009, accompanied by strong convective weather phenomena such as disastrous wind and hail. The developing processes of the two gust fronts were analyzed based on Doppler radar data, radiosonde data, surface meteorological observation data and Aircraft Meteorological Data Acquisition and Relay (AMDAR) data. The results indicate that the strong vertical wind shear in background field intensified the growth of convective cells in the squall line and made its inclining. The westerly cold flow, entering the back of squall line, stimulated the convective activities of the cells and gave birth to the first gust front. The acceleration of westerly surface flow, produced by the great temperature gradient of a northerly cold flow and the warm core of the squall line is the instant cause for the genesis of the second gust front. The lineshaped convergence zone was formed in the major body of the squall line moved to the second gust front， which became a new squall line finally.