Abstract: The study of the relative motion between particles and bubbles is critical to the understanding of flotation mechanism. At present,the research on the relative motion between particles and bubbles is mostly based on theoreti- cal analyses. The experimental research is relatively limited and the test objects are particles with regular shape and homogeneity properties. In this experiment,the coal samples from Gongwusu mining area in China was taken,and the relative motion between particles and bubbles with the particle size of 0． 100-0． 074 mm and densities of -1． 3,1． 4-1.5,+1． 7 g / cm3 was studied by self-designed experimental device. During the test,the trajectories of a large number of coal particles were traced. The change laws of particle motion parameters during the settlement stage,the deviation stage and the collision stage were studied. The experimental results show that the equivalent diameter of particle is 0． 092 mm. The particles reach the terminal velocity after transient acceleration and the terminal velocity of particle in- creases with the increase of particle’s equivalent diameter and density. Bubble will affect the trajectory of particle. Inthe same initial settlement interval,the vertical distance between the deviation point of particle trajectory and bubble decreases with the increase of particle density. The main dis-tribution interval of collision angle is 20°-50° in hydro- static conditions. The collision interval and particle con-centration interval expand outward with the expend of initial settlement interval. When the collision angle is less than 50°,the reduction ratio of particles collision velocity decreases linearly with the increases of collision angle. When the collision angle is greater than 50°,the reduction ratio of particle velocity tends to plateau. The velocity reduction of low-density particles is greater than that of high-density particles, but the difference is not obvious. The theoretical calculation shows that the theoretical collision velocity is small when the particle initial settlement position is closer to the central axis of bubble. The particle theoretical collision velocity increases with the expend of initial settlement interval,which has a good agreement with the experimental results.