Solar energetic particle events is a major concern of Space Weather. We develope a SEPCaster model to simulate the acceleration and transport of solar energetic particles in gradual SEP events. SEPCaster combines the AWSoM and the iPATH codes with the AWSoM code providing a physical description of the solar wind and the coronal mass ejection (CME), and the iPATH code treating the acceleration and transport of energetic particles. Using SEPCaster, we investigate particle acceleration when the CME-driven shocks are still close to the Sun and obtain reasonable agreements between our simulation and observations for individual events, at multiple spacecraft. By varying the model parameters, we identify important parameters that control the production of energetic ions in large SEP events.