Direct radiative forcing of aerosols takes an important role in the global radiation budget and thus global climate change. The Intergovernmental Panel of Climate Change (IPCC) estimates the aerosol radiative forcing lies between -0.26 and -0.82 Wm^-2. The most recent satellite analysis suggests a direct forcing of -1.9 ± 0.3Wm^-2 of anthropogenic aerosols that is significantly higher than the current model results. The uncertainty in estimating direct radiative forcing of anthropogenic aerosols in the models clearly exists and this is likely caused by various arbitrary simplifications and parameterizations in calculating aerosol related processes and in radiation calculations. In order to better understand the roles of aerosols in climate, an interactive aerosol-climate model has been developed by incorporating a chemistry and size-dependent aerosol model into the National Center for Atmospheric Research Community Atmospheric Model, version 3 (CAM3). For the present study four different types of anthropogenic aerosols, namely black carbon (BC), organic carbon (OC), sulfate (SO₄), and mixed aerosols (BC/SO₄) are included in the model in six aerosol modes (3 for sulfate aerosols). Size- and chemistry-dependent aerosol physics and chemistry are formulated. We have evaluate the spatial and seasonal distributions of aerosol concentrations using satellite and surface observations to derive a possible constrain of the model in further climate change study. The global radiative forcings of various aerosols are then calculated using predicted information of aerosol size distributions and these modeled results are then examined using observations. The modeled impact of anthropogenic aerosols on global and regional climate will be discussed.