The 5G core network adopts Network Functions Virtualization technology, which forms a variety of virtual resources for general computing, storage, and network hardware to achieve dynamic and flexible deployment of network functions and resources based on needs. With large-scale commercial deployment of cloud-native 5G core network with network function virtualization technology, the operation and maintenance of 5G core network is facing new challenges. This paper describes the architecture and deployment characteristics of 5G core network, and analyses the challenges brought to operation and maintenance by new network characteristics such as SBA, NFV, MEC and separated UPF, as well as the difficulties of operation and maintenance of virtual deployed 5G core network. Combined with the architecture evolution and function enhancement of 5G-Advanced, the architecture and scheme of A Novel Intelligent 5G-Advanced Core Network Operation and Maintenance System are proposed. The architecture and scheme of 5G core network operation and maintenance system construction were proposed, and suggestions on the organizational structure of 5G core network cloud-network integration operation and maintenance were put forward, so as to provide reference for 5G core network cloud-network integration operation and maintenance. The proposed scheme improves the performance of operation and maintenance of 5G core network significantly.