A network element registration method and system, and a Network Function Repository Function (NRF) are disclosed. The network element registration method may include: receiving, by a Network Function Repository Function (NRF), a registration request of a NRF extra-domain service provider network element, the registration request includes service identification information of the NRF extra-domain service provider network element; and allocating, in response to the registration request, a first network element instance ID for the NRF extra-domain service provider network element, the first network element instance ID is different from a second network element instance ID allocated by the NRF for a NRF intra-domain service provider network element.