Abstract: This study assembles a pipeline mist spraying experiment rig and measures the motion characteristics of wa- ter mist in the square pipeline using Particle Image Velocimeter. It explores the settling law of water mist in the pipe- line with various spraying pressure and airflow velocity and analyzes their influences. The results indicate that the set- tling volume increases by 96% in the 1 meter long downstream pipeline,when the spraying pressure increases from 0． 1 MPa to 1． 3 MPa at a set airflow velocity,which is mainly caused by impinging. And the settling volume reduces by 76% in the other parts of the pipeline,which is caused by inertance. But when airflow velocity increases from 1.1 m / s to 10． 4 m / s with a set spraying pressure,the settling volume reduces by 24% in the 1 meter long pipeline and reduces by 17% in the other parts. The results will provide a reliable theoretical basis for gas explosion suppres- sion and the parameter setting of water mist in the safe transportation of low concentration gas.