Abstract: The problem of water hammer of the Ansai-Yan'an pipeline with closed transportation system is discussed. The water hammer pressures of four kinds of trarisient processes are determined through simulation and pressure variation curve maps are drafted. The results show that for closed transportation system of Ansai-Yan'an pipelines regulating valve should be installed in the outlet of Yanhewan station and a low pressure relief system and a back flow pressure protection system must be set in the inlet of the station; a relief valve should be installed in Yangshan station, and low pressure alarm system is needed for each station. Safe operation of the pipeline can be accomplished through local control and manual regulation.