This paper presents a large scale hydrological model for the Fitzroy Basin using the MIKE 11 NAM modelling system. This model simulates the rainfall runoff processes for the three different and interrelated storages which are surface storage, root zone storage and groundwater storage. The parameters of such model cannot be obtained directly from measurable quantities of catchment characteristics. Hence model calibration is required to get the model parameters. Manual calibration is very time consuming and it only focuses on a single objective function. Thus tradeoff exists between the different objectives. For this study, an automatic calibration was done considering the four multiple objectives and obtained the optimal values of the model parameters for each catchment. The simulated and observed discharge hydrographs show a reasonable good match for each sub-catchment. Moreover model reliability was evaluated using the statistical methods Index of Agreement (IA) and Efficiency Index (EI). The IA and EI obtained 0.821-0.951 and 0.849-0.961 for different sub-catchments.