Abstract: In order to clear away the foreign materials, hydrops and impurities, enhance the transport efficiency, reduce the friction loss and corrosion of inner pipe wall, extend pipeline lifespan, pigging is necessary periodically. The pigging cycle is selected on the basis of analyzing pipeline parameters and in consideration of security, economic, social and other factors to get a proper scheme. Based on the investigation of pigging cycle determination methods of trunk pipeline in China, and the actual conditions of Yulin-Jinan Gas Pipeline, gas transmission efficiency is adopted to measure the pipeline running state, meanwhile pressure drop is taken as the index for pigging. Calculation model of gas transmission efficiency for the pipeline is established based on PR equation, C-W formula, and the relationship between gas transmission efficiency and pressure drop is obtained. According to the correlation chart of gas transmission efficiency and pressure drop, pigging cycle can be figured out, and reasonable and abnormal condition of pipeline inside can be judged and controlled through the real time monitoring the pressure at both ends of each section.