Abstract: Objective As the vital link connecting central urban areas with peripheral clusters, city（suburban） railways play a crucial role in promoting the integrated development of rail transit network. Therefore, a systematic study on the interoperation between city（suburban） railways and multi-level rail transit networks is necessary. Method The development models and key characteristics of rail transit interoperability in major international cities such as Tokyo and Paris, and technological innovations in technical standards and operational management in Chinese cities including Shanghai, Beijing, and Chongqing are introduced. The principles and technical key points for interoperation between city（suburban） railways and multi-level rail transit are proposed. Result ＆ Conclusion The interoperation between city（suburban） railways and multi-level rail transit systems should follow six principles: time efficiency advantage, significant passenger demand, adequate line capacity, acceptable construction cost, compatibility of technical standards, and coordination in operational management. The technical key points for interoperation are proposed from three levels of technology, operation and organization. Technically, compatibility of standards is achieved through dual-mode power supply and signaling system modifications; operationally, coordination efficiency is enhanced via regional dispatching centers and integrated ticketing platforms; organizationally, unified transport is realized by optimizing train routing and passenger guidance signage.