Abstract: When pigging running is carried out for mountain gas pipeline, the influence of changed gravitational potential energy induced by the differences of elevation on hydraulic calculation and that of water pressure resistance within the pipe on the travelling speed of pig must be taken into consideration. According to the standard of SY/T6383-1999 and referring to the pigging practice in Fenyang-Wuxiang pipeline section in Yu-Ji Gas Pipeline, a statistical analysis on travelling speed of pig and pressure differences of pipeline section for 5 pigging runnings is made in this paper, and the influences of water pressure resistance, slugging flow and severe slug flow induced by the differences of elevation on pigging running are summarizes. By setting up mathematical model to simplify the calculation formula for water pressure resistance, the authors establish the functional relationship for computing the accumulated water length in different pipeline sections.Technical requirements in pigging running for large diameter and high pressure pipeline at mountain areas with in-line pigging mode are given.