Abstract: In the pigging process of long-distance gas-liquid pipelines, seal disc diameter of pig may be less than the internal diameter of the pipeline due to abrasion. To research pigging process characteristics of pigs with different pigging diameters, 2 straight pigs with different diameters are used to conduct the air-water two-phase flow pipeline pigging simulation experiment in the transparent plexiglass tube experiment loop. The results show that medium flow in the pipeline could be divided into 4 zones, pig speed continuously changes and average speed is closed to the gas-liquid mixing speed when the pig diameter is greater than the internal diameter of the pipeline. When the pig diameter is less than the internal diameter of the pipeline, and gas-liquid two-phase media are in the upstream and downstream of the pig, pig movement suffers from a larger impact from the liquid phase media and the average speed fluctuates greatly and is lower than the gas-liquid mixing speed. The speeds and lengths of pigging liquid plugs are detected and calculated, showing the better consistency between the calculated values and detected results.