A system for realizing the number carrying service between mobile networks and a method are provided, wherein the system is formed by an independent number carrying database SRF-NPDB and a local service management system LSMS, which have the SPF function, and both are accessed into a number seven signaling network. A global office number translation point office data pointing SRF-NPDB is arrangedin a related mobile exchange center, and the SRF-NPDB changes and transforms the number of a number carrying user for realizing the purposes of addressing and continuous controlling, and the LSMS is used to manage the number mapping relation of a local portable user, and synchronizes with the SRF-NPDB. The invention has the characteristics that the number carrying service can be fairly and independently carried out through adopting an independent network element device by the data setting of exchange nodes without transforming the current signaling transfer point STP, which avoids the tight coincidence with the STP, guarantees the communication service quality, and provides an effective method for independently opening the number carrying service between the mobile networks.