Assessment of rainfall runoff for an event given is a challenging task due to various controlling factors. Many computer depended hydrological model have been developed for simulation of runoff in watershed and water resource studies. In this study, Soil Water Assessment Tool (ArcSWAT) an extension tool has been used to simulate runoff process in Walnut Gulch watershed located in Arizona, USA over sub hourly base. For computing infiltration, excess rainfall conversion to runoff and flow routing, methods like Green and Ampt method are adopted and the sensitive parameters that influence the model are identified. The model has been calibrated and validated for the five rainfall events. From the results obtained, we can assume that the ARCSWAT model has performed satisfactorily for the runoff simulations for differed rainfall events.