Abstract: In this paper, the foaming mechanism of the laser marking of black PBT material was studied, and the corresponding mathematical model was established. The theoretical analysis indicated that the main factors affecting the laser marking effect of black PBT material included the coverage of bubbles, the absorption coefficient of bubble wall, and the height and diameter of the bubble hole. The model analysis suggested that the test light reflected, refracted and transmitted on the surface of the bubble when irradiated on the laser marking area. The coverage of bubbles was considered as the main factor affecting the lasermarking effect. It is found that the L value of the laser marking increased from 42.6 to 72.8 by adjusting the coverage of bubbles, and meanwhile the value of ΔE was improved from 15.1 to 42.8.