Abstract: Secondary flow is a common physical phenomenon in engineering practice, which is a secondary flow relative to the mainstream. In order to study the influence of secondary flow on airflow velocity and different particle sizes of sand particles in a sand sampler, this paper uses a combination of numerical simulation and experimental verification to analyze the flow field characteristics before and after secondary flow is weakened, taking the wind-sand separator of the shunt-hedging and multi-stage expansion sand sampler as the research object. The research results indicate that before secondary flow is weakened, sand with a particle size greater than 0.083 mm are completely collected, while sand with a particle size less than 0.083 mm are mostly collected. After secondary flow is weakened, the distribution range of high-speed airflow becomes larger, and the flow field seems to become unstable. The airflow velocity inside the exhaust pipe significantly increases, and only sand with a particle size greater than 0.12 mm are completely collected, and the range of sand being completely collected is significantly reduced.