In order to improve the security of power dispatching data transmission over the network, the combined modulation quantum key distribution system which encodes each single-photon signal with both phase modulation and polarization modulation is studied. Based on the abstract unit model of power dispatching data transmission network, the network deployment scheme of using quantum key to realize the encrypted transmission of dispatching data is elaborated. In order to better meet the needs of practical application scenarios, a quantum key allocation scheme that comprehensively considers service importance, service bandwidth, and the amount of remaining keys in the quantum key pool, a quantum key request response scheme that comprehensively considers service delay constraints, the number of service key requests and service importance, and a quantum key pool key resource supplement scheme that comprehensively considers the success rate of service encryption and the freshness of quantum keys in the quantum key pool are further designed. The scheme presented in this paper can provide a reference for the design and practical application of quantum secure communication network for power dispatching data.