A network slice instance management method, an apparatus, and a system. The method includes: determining, by a first network device, that a configuration parameter of a first network slice subnet instance needs to be modified, where the first network device is configured to manage the first network slice subnet instance; modifying, by the first network device, the configuration parameter of the first network slice subnet instance; and sending, by the first network device, report information to a second network device, where the report information is used to indicate a result of modifying the configuration parameter of the first network slice subnet instance, the second network device is configured to manage a first network slice instance, and the first network slice instance includes the first network slice subnet instance.