Abstract: To improve the probability of collision and coagulation among ultrafine particles, a tangential swirl coagulation device was developed, in which the flow field and particles moving trajectory were simulated using discrete particle model (DPM), so as to analyze the influence of swirl velocity, particle size and acoustic wave on the moving trajectory of particles. Results show that the tangential swirl has good swirling and mixing effects that benefit for the collision and coagulation of ultrafine particles; the higher the swirl velocity is, the stronger the swirling effects will be on the particles, leading to easier collision and coagulation among particles. Ultrafine particles of large sizes are subjected to large centrifugal force, which are more likely to mix with the seed particles, while those of small sizes are subjected to small centrifugal force, which are more likely to mix with the ultrafine particles of similar sizes. Acoustic wave can enhance the relative motion among particles of different sizes, which make ultrafine particles easier to collide and coagulate with the seed particles.