A method supporting enhanced network identity (NID) provisioning under User Equipment (UE) mobility scenarios between different types of networks is proposed. When a UE registers to an SNPN, the UE is assigned with a 5G-GUTI by the SNPN. The SNPN is identified by an SNPN ID==PLMN ID+NID. When the UE moves from the SNPN to another target network having a target AMF, the UE triggers a mobility registration update procedure and provides the 5G-GUTI along with NID information in a Registration Request to the target AMF. The target AMF can use the NID information along with the 5G-GUTI to find a source AMF for deriving UE context for the subsequent operations during the mobility registration update procedure. Providing NID information along with 5G-GUTI can assist the target AMF to find the source AMF efficiently, preventing a potential registration procedure failure.