Abstract: The effects of different convective parameterization, explicit moisture schemes and surface heating on the simulation of the meso-β scale structure of a squall line system are investigated using an improved meso-scale model. It is found that the successful prediction of meso-scale convective systems hinges upon not only the sub-grid scale convection, but also the resolvable scale phase change processes and the diurnal variation in the boundary layer. The simultaneous operation of the Fritsch-Chappell convective scheme with parameterized mois downdrafts and the prognostic equations for cloud water (ice) and rainwater (snow) seems to be essential in simulation realisticly MCSs and reducing or eliminating the unrealistic development of the CISK-like instability associated with the squall line system.