Abstract: When undulating wet gas pipelines are in operation, liquid loading tends to occur at low-lying and ascent sections of pipelines, and consequently leads to a series of problems. These include the reduction of pipeline transmission efficiency, the increase of pipeline pressure drop, the generation of hydrate, the formation of slug flow and the aggravation of pipeline internal corrosion, etc. In this paper, therefore, the liquid loading laws of undulating wet gas pipelines were analyzed. The distribution situations of liquid along undulating wet gas pipelines were investigated by taking the gathering pipeline at a certain gas gathering station as an example. And sensitive analysis was performed to the effect of gas flow rates and pipe inclination angles on liquid holdup of the undulating wet gas pipeline. Consequently, the liquid loading laws of this undulating wet gas pipeline were understood and the critical inclination angle at which no liquid loading occurred at a certain flow rate was cognized. Afterwards, a mathematical model used to predict the relationship of liquid holdup, gas flow rate and pipe inclination angle was built up. Its accuracy was verified by comparing its calculation results with the simulation data of software. It provides a theoretical basis for the liquid loading control and safety of wet gas pipelines during their operation.