A universal and flexible network architecture is required to meet the demands for wide area coverage and optimal user experience in 6G. In this paper, a powerful network architecture, user-centric access network (UCAN), is proposed to meet the multi-dimensional demands of 6G. After analyzing the motivations and requirements, we introduce the concept, architecture, and networking scenarios of UCAN. UCAN has four distinct features including deeply customized network, elastic reconfigurable network, open and compatible network, and intelligent adaptive network for user-services. In deployment, flexible cell can be constructed and updated for a user with the suitable surrounding access points. The challenges and corresponding key technologies to achieve UCAN are then illustrated, which includes user-centric access and connection management, dynamic AP management, unified management of interference and resource, and lightweight security. Finally, a simulation result is given to verify the effectiveness of UCAN and future works are discussed to indicate the research directions for academia and industry.