The access of high proportion of new energy poses a challenge to the stability of the system, and it is of great significance to study the DC feeder system with asynchronous networking to ensure the large-capacity and stable transmission of the DC channel under the proportion of new energy. Introducing system voltage and frequency support capabilities, with the optimization goal of maximizing system external transmission capacity and new energy consumption capacity, and minimizing the imbalance of voltage support capacity, the DC external transmission capacity improvement optimization model based on the optimization of the sending-end system support capacity is established by introducing the system voltage and frequency support capacity. The model is divided into main and sub-problems, and the IMOPSO-PSD joint optimization simulation algorithm based on the improved multi-objective particle swarm algorithm is used to solve the model, and the optimal operation mode is screened out by the coefficient of variation method taking into account the imbalance of the voltage support capacity. Finally, the effectiveness of the proposed method is verified by taking the IEEE 39-node asynchronous DC sending-end grid model with high proportion new energy as an example.