The purpose of this paper is to investigate the interaction between dispersed and elongated bubbles in horizontal slug flow utilizing the laser-induced fluorescence method. A segmentation method based on the fuzzy C-mean (FCM) algorithm is proposed to effectively separate elongated bubbles from the liquid phase, and an extreme value extraction method is developed to calculate the number of dispersed bubbles in front of the nose of elongated bubbles. Moreover, the velocity offsets of elongated bubbles with and without dispersed bubbles are calculated separately based on contour extraction. In addition, the effects of dispersed bubbles on the fluctuating offsets of the nose tip position and velocity of elongated bubbles are statistically investigated under different flow velocities. The experimental results show that the increase of the gas-liquid flow velocity exacerbates the radial deviation of the nose tip and the fluctuation of axial velocity.