Abstract: The traditional light scattering measuring device could be polluted easily by dust. This study simulates the gas-solid two phase flow using Fluent software,and thus designs a more rational structure based on the influencing fac- tors which are found from the analysis of particle trajectories. The numerical simulation experimental data shows that the low-velocity vortex is due to scouring the measurement structure by gas for a long time,and becoming polluted. A new structure is designed,which cannot be polluted easily. The experimental results show that this new design makes gas pass the channel speedily and form a turbulent vortex,so dust cannot be detained in the measuring device. This can ensure the veracity and timeliness of the measuring device.