Abstract: Spatio-temporal slice is an efficient spatio-temporal analysis method. However, the literatures are limited to simple straight trajectory processing, which cannot fulfill complex trajectory handling in real-world scenarios. To solve this problem, this paper presents a real-time spatio-temporal slice complex trajectory analysis algorithm to track human motions. First, horizontal slices at different heights are extracted from the surveillance videos. Gaussian background modeling is carried out to detect human trajectories in these slices. Then, after combining all trajectories from different slices, Hough transform is employed to compute the combined trajectory equations. Finally, humans’ positions as well as widths and heights are obtained based on the equations and trajectory detection results. Compared with traditional tracking approaches, experimental results show that our approach reduces trajectory errors, satisfies real-time tracking requirement and has abilities to track humans under short-time occlusions.