Abstract: The technology of particles aggregation is a kind of effective method to strengthen the ultrafine particles collection.The flow field of the turbulence coalescence device was simulated by FLUENT,and the results show that both big and small vortex chips are good at producing vortices,which could creat favorable conditions for the collisions and coalescence of the ultrafine particle.The simulation of the ultrafine particles trajectories which carried out at different velocity,different size and charged or not,led to a regular conclusion: the faster the velocity is,the larger particles affected by the turbulence,and it is easier for the collisions and coalescence;large particles are less effected by the turbulence,while the small ones are effected more,so there is an apparent relative motion between them;the attractive force between particles increases as the particles are charged,which make it easier for the collisions and coalescence.