Abstract: A real-time quasi-geostrophic omega diagnostic scheme, based on Hoskins′-vector analysis, is applied to a MCC (mesoscale convective complexes) with severe convection over northeast China in summer. And the vertical motion of the system is computed by use of the ten-level meso- scale nonlinear model. The principle results are as follows: thermal advection is an initial triggering condition for the genesis of this MCC. The cumulus heating and large –scale latent heat release are, generally, very crucial physical factors for the intensification and development of the system. The divergence and the rotational component of the -vector and the geostrophic frontogenetical function expressed by -vector would provide forecasters with a lot of useful information.