Network slice security is the prerequisite for introducing network slicing to vertical industries. There is gap between slice security requirements and different security capabilities that need to be provisioned during the slice lifecycle. An intelligent 5G slice security capabilities provisioning method is urgently needed to help provision the most suitable security capabilities of one slice dynamically according to the network status and the security target. This paper proposes digital-twin-based basic security functions and an autonomous 5G slice security capabilities provisioning solution in order to achieve KPI-driven dynamic slice security provision.