In order to study the interaction between particles with different sizes in a cyclone separator and the influence of coarse particles on the separation efficiency, the local flow at the inlet of the separator is simplified as a wall-attached jet, and the coarse particles are idealized as rigid spheres. The method of large eddy simulation and discrete phase model coupling is employed to study the disturbance of near-wall balls on micron-sized particles for gap ratios of 0.125, 0.25 and 0.5 between the ball and the wall. The results show that the flow field fluctuates significantly in the characteristic attenuation region of the jet (θ=20°-75° in the circumferential direction). In the range θ=20°-30°, with increasing gap ratio, the tangential velocity distribution behind the ball gradually approaches that without the ball. When the gap ratio is 0.5, the difference between the tangential velocity distribution and that without the ball is the smallest. When the gap ratio is 0.25, the peak value of vorticity in the wake vortex area behind the ball is the largest, and the ball has the maximum influence on the intensity of the jet flow direction vortex. For particles with d_p=125-250 μm, the ball has little effect on the residence time or the number of escaped particles. Compared with the absence of the ball, the average residence time of particles with d_p=125-250 μm is reduced, the percentage of escaped particles is increased, and the separation efficiency is improved. When the gap ratio is 0.25, the residence time of particles is the shortest, and the percentage of escaped particles is the highest.