A method, device and system for implementing optimized inter-RAT handover are disclosed. In the method, a user equipment or a source network decides to prepare for a handover to a target network. A corresponding target network ID is obtained from a configured mapping between cell IDs and target IDs according to a received cell ID. Target network bearers are set up after determining an access node of the target network. The user equipment is connected to the target network after handover preparation is complete.