Abstract: With the increasing penetration of heterogeneous resources on the demand side, such as distributed generation, electric vehicles, and thermostatically controlled loads, it is urgent for them to participate in grid dispatching and control. A virtual power plant (VPP) is an effective form to aggregate and control massive distributed energy resources (DERs) while the simulation tool is crucial for its practical application. In this context, a VPP short term refined production simulation method covering DER device modeling, heterogeneous DERs aggregation, and cooperative control between clusters is presented. An open simulation system for VPPs participation in grid interaction is designed. First, the requirements and key technologies of VPP's short term refined production simulation are summarized. Then, a refined modeling of VPP considering both equipment layer and control layer is proposed based on the analysis of physical characteristics and control algorithm. After that, the simulation system following the principle of generalization and openness is designed, and it is compatible with a variety of grid simulation engines and a variety of DER models by modular modeling, universal architecture, and interactive interface design. Finally, the simulation results of a single VPP production for a typical day, the power response dynamics of DERs clusters as well as the effects of VPP in frequency emergency control and rotor angle stability emergency control are given to verify the effectiveness of the method and the system proposed.