The invention discloses a quantum security gateway key offline updating method, which comprises the following steps that a quantum random number management platform, a first quantum key service terminal and a quantum security USB key are deployed in a quantum security basic service center, and a second quantum key service terminal is deployed in a service desk; the quantum random number managementplatform generates a quantum key through a quantum random number generator and inputs the quantum key into the first quantum key service terminal and the quantum security U shield at the same time; the first quantum key service terminal and the quantum security U shield receive the quantum key input by the quantum random number management platform and synchronize the quantum key, and after the quantum key input is completed, the consistency of the quantum key is verified; and after consistency verification is completed, the quantum security USB key is safely transported to a service desk andis inserted into the second quantum key service terminal. On the premise of not damaging the original network structure, the communication security of the power service is improved, and the long-timeand high-speed key updating and use of the service can be met.