When multiple inverters are connected to the grid, the interaction between the inverter and the grid results in coupling resonance in the grid connected system. This affects the stable operation of the system. In order to reflect the resonance characteristics of a multi-inverter grid connected system, this paper establishes the corresponding equivalent model which fully considers the influence of relevant parts in the grid connected system on the resonance characteristics of multiple inverters based on single inverter grid connected Norton model. It analyzes the influencing factors on the resonance point in detail. In the control system, the capacitor series virtual resistance is used to suppress the resonance of the grid connected inverter system. The optimal value method of the virtual resistance value is proposed, and the value and the effect of the equivalent model resonance suppression are analyzed. Finally, the correctness and effectiveness of the proposed equivalent model and optimization method are verified by simulation. This work is supported by the Key Project of Smart Grid Technique and Equipment of National Key Research & Development Program of China (No. 2016YFB0900601), the Science and Technology Project of State Grid Corporation of China (No. 52094017000W) and the Regional Innovation and Development Joint Fund of National Natural Science Foundation of China (No. U19A20106).