In order to evaluate the performance and select the filtration and separation equipments used in natural gas distribution station，a particular pressure reducing device was designed by using throttling effect.An on-line dust measurement method in high-pressure natural gas pipeline was proposed.Numerical calculation and experiment result show that there is no liquid droplet generated during pressure reducing.The influence of the pressure-reducing device on particle concentration and size distribution can be ignored.The method of dust on-line measurement in high-pressure natural gas pipeline is accurate and reliable.