This paper studies a thunderstorm event detected by Doppler Weather Radar(CIN RAD WSR/98D) in Tianjin on 13 August 2007,showing that the thunderstorm event is triggered by collision between sea breeze front and gust front over Bohai Bay.After the collided,new thunderstorm cells formed in the front of sea breeze front and gust front.The convection echo body intensifies in the back of gust front,and changes from theellipse echo to the typical bow echo.This paper applies the ground data of six factors at 36 automatic weather stations in Tianjin and the sounding data above 850 hPa in Beijing,forming new diagnostic data.Diagnostic analysis shows that there are strong low-level vertical wind shear and dew point temperature gradients in the front of sea breeze front detected by the Radar.The front edge of sea breeze front corresponds with the dense area of 0—3 km vertical wind shear gradient,and basically tallies with the rapid change zone of dew point temperature gradient.When the sea breeze front and the gust front collide,the 0—3 km vertical wind shear changes rapidly within 2 h with an obvious increasing trend,and CAPE(convective available potential energy) has significantly increased before the formation of thunderstorm.With the end of thunderstorm,above features will disappear.