Abstract: To deal with the challenges brought by the large scaling and complication of natural gas pipeline networks, promote the safe operation, and improve the quality and efficiency through fully using the data achievements obtained in pipeline automation and digitalization, online simulation is becoming an urgent and important means for the scheduling management and operation control of pipeline networks, attracting wide attention from the nation, enterprises and society.The development of online simulation system for pipeline networks and the project implementation are the integrated application of many fields of theories and technologies, in which numerous problems and factors such as simulation theories and methods, software and technologies, data and automation, scheduling and management, operation and control, maintenance and upgrade, etc. are involved, directly reflecting the latest research results of science and the engineering experience in the relevant fields. Herein, the macro and overall structure, level and function of online simulation system of pipeline networks were discussed based on many years of research, development and application practices. Meanwhile, exploration was performed on the theories and methods, software and core technologies, and important concerns regarding system construction and implementation of the online simulation system. In addition, the application process and effect of current research achievement of online simulation were presented based on the practical application cases of Sichuan-to-East Gas Pipeline and the subsea long-distance gas pipelines in western South China Sea, with the expectation to promote the research, development and application of online simulation of natural gas pipeline networks in the future.