Abstract: Natural gas pipeline system simulation is the core technology for design plan demostration, transportation plan development, operation plan optimization, and emergency security decision-making of pipeline system. Hence, a simulation model applicable to the pipeline network systems in any structures was established based on the principles of conservation of mass, momentum and energy, as well as the characteristic equation of non-pipe elements. An algorithm for solving the simulation model of pipeline network system was formed based on the functional analysis of pipeline mathematical model and the fast LU decomposition under the large sparse matrix compression storage conditions. Besides, large-scale online simulation software for natural gas pipeline systems, comprising the modules of data communication, database storage, data filtering, online simulation and result pushing, was developed with the B/S software architecture, the big data caching technology and the real-time visualization technology for big data extraction. Then, the software was applied in a pipeline network system with a total length of 6 100 km and 45 compressor stations and a large pipeline network system with a total length of 31 000 km and 117 compressor stations. It is indicated that the applicable scale, calculation accuracy and speed of the software have reached the international level of similar commercial software.