A warm cloud microphysical parameterization was incorporated into a regional model to study the sensitivity of cloud-radiative properties and precipitation to aerosols. Assuming a tri-modal lognormal aerosol size distribution, the aerosol numbers are explicitly calculated from prognostic aerosol masses, considering advection, diffusion, and cloud and rain drop activation/deactivation processes. Sensitivity experiments of a cold front passing through northern China during 25－27 June 2005 with different initial conditions for clean, continental, and urban types of aerosols were then conducted to study the Giant Cloud Condensation Nuclei (GCCN)’s effects. It is found that the presence of giant nuclei enhances the condensation, collection, and cloud-rain auto-conversion process, leading to the decrease of cloud drop numbers and cloud water by 40% and 20% respectively, to the increases of cloud drop radius by 30%, and increases accumulated precipitation both in polluted and clean environment.