A severe convection event in the plain of Hebei on May 10, 2005 is investigated from such aspects as synoptic situation，physical mech anism，radar echo and satellite image evolution，and the Taihang Mountain forcin g, etc. by using the NCEP reanalysis data, conventional observations and the dat a from automatic weather stations，Doppler radar，Fengyun2C satellite images. The result shows that the severe convection weather arise in the transition from verticality to forward slant of the upper trough，so there was a different advec tion between the mid(cold and dry) and lower (warm and wet) troposphere，whi ch was quite important to the formation and development of convective instability. The event was triggered by the surface low and mesoscale convergence line，an d the squall line was direct influencing system.. It is also found t hat the severe convection area had a better corresponding relation to the high potential pseudoequivalent temperature (θse) at lower level，large water vapor fl ux，strong convergence and upward current，and high convective available potential energy ( CAPE) during this event.