Large-scale energy storage can be used to solve the transient voltage problem caused by high penetration of renewable energy resources. Therefore, it is necessary to study the optimization method of the configuration scheme of energy storage devices. This paper investigates the transient voltage stability of a HVDC sending-end grid containing large-scale new energy sources. By optimizing the capacity configuration of energy storage, the transient voltage stability of the HVDC sending-end grid is significantly improved. Firstly, the over-voltage phenomenon in the actual grid is introduced and the causes of this phenomenon are analyzed. Then, the capacity and parameter optimization methods of energy storage are proposed, including the calculation of grid reactive-voltage index, and the iterative optimization method of capacity configuration driven by electromagnetic transient (EMT) simulation. Finally, the correctness and feasibility of the proposed method are verified by using by using the EMT model of the actual grid.