Abstract: Lanzhou-Chengdu Crude Oil Pipeline is characterized by long distance, high pressure and great fall. During its commissioning, it is partially filled with water at normal temperature and then the water is displaced by oil. This paper makes a brief introduction of Lanzhou-Chengdu Crude Oil Pipeline and illustrates the preparation for its commissioning. This paper further describes the process of the commissioning, including partial water filling of pipelines, leak detection by shutting down for pressure building and oil filling. Moreover, it provides a detailed description on water filling length, intermediate station blowdown, high exhaust, especially the leak detection by shutting down for pressure building that is initially carried out by sections in large-size oil pipeline. Some suggestions are proposed on unity of surge protection, necessity of intelligent caliper before commissioning, and issues (e.g. different pressures of oil and gas, and airlock) during commissioning. Finally, this paper presents the significance of partial water filling and leak detection by shutting down for pressure building, and provides practical reference for the commissioning of subsequent liquid pipelines.