Embodiments of this application provide a key generation method, applied to a scenario in which a base station is divided into a centralized unit and a distributed unit and a control plane and a user plane of the centralized unit are separated. And the control plane entity of the centralized unit obtains a root key, generates a user plane security key based on the root key, and sends the first user plane security key to the user plane entity of the first centralized unit. According to this application, key isolation between different user plane entities is implemented. Further, in an actual operation, the control plane entity or the user plane entity of the centralized unit may be flexibly selected to generate the user plane security key.