The flotation microscopic model considers that the attachment behavior of coal particles and bubbles is the key step to achieve flotation. Therefore, the direct research on attachment behavior is very important. A device was designed by ourselves to directly measure the attachment behavior of coal particles and bubbles. In this paper, the raw coal of Inner Mongolia Gongwusu was taken as the experiment subjects and the attachment behavior of 0. 1-0. 15 mm coal samples with different densities was directly observed. Then, it was analised by the multi-target tracking software. The results showed that coal particles would flowed around the bubble before collision occurrence, and the velocity and direction of coal particles would changed. The velocity of coal particles decreased to minimum when coal particles colliding with bubble. The sliding velocity of coal particles on the bubble surface firstly increased gradually, and sliding velocity reached the maximum at the bubble "equator" position. After crossed the "equator", the sliding velocity of coal particles gradually decreased, and finally coal particles attached to the bottom of the bubble. The attachment efficiency of coal particles and bubbles decreased with the increase of collision angle. At the same collision angle, the attachment efficiency and the critical attachment angle decreased with the increase of coal density. With the increase of terminal velocity, both the attachment efficiency and the critical attachment angle decreased. Therefore, the regulation of the attachment efficiency of different density was verified. [ABSTRACT FROM AUTHOR]