Joining dissimilar materials is required in many engineering applications and conventional fusion welding of dissimilar materials often results in defective welds. Friction Stir Welding (FSW) has paved way for joining dissimilar alloys and defect-free joints have been obtained for a number of dissimilar material combinations. Numerical modelling of FSW process can provide reasonable insight into the physics of the process and will aid in minimising the number of experimental trials. In this paper, Computational Fluid Dynamics (CFD) based numerical model is developed to predict the temperature distribution and material flow during FSW of dissimilar aluminum alloys AA2024 and AA7075. Volume of fluid approach is used and the FSW process is modelled as a steady-state visco-plastic laminar flow past a rotating cylindrical tool. Results indicate that peak temperature in the welded plates increases with the increase of Tool Rotation Speed (TRS) and Shoulder Diameter (SD), whereas the peak temperature decreases with increase in Welding Speed (WS). Increasing TRS and SD increases material flow, while increasing WS decreases material flow in the stir zone