Slug flow in inclined pipes is commonly observed in hilly terrains and oil well production, where changes in the angle of inclination can alter the behavior of the slug flow. To better understand the impact of inclination on slug flow, this paper investigates the characteristics of slug flow in inclined pipelines based on the laser-induced fluo-rescence technology and image processing method. A two-dimensional Otsu method based on particle swarm op-timization algorithm is proposed, which achieves fast and accurate segmentation of gas-liquid interfaces. Moreover, the effect of the inclination angle on flow characteristics is discussed. Experimental results show that the inclination angle significantly impacts the translational velocity, the tail interface of elongated bubbles, and the distribution of liquid film thickness.