There exist many problems such as high pigging velocity and long pigging slug in the pigging process in natural gas liquid pipelines by using traditional pig. In order to solve these problems, bypass pigging technology has been developed. To analyze relevant factors in the design and application of bypass pig, a subsea pipeline pigging model is built by using OLGA software (version 7.2) and the factors including bypass ratio of the bypass pig, pipe diameter, gas liquid ratio, pig weight etc. have been analyzed, which can provide reference for the design and application of bypass pig.