Three infrared couplers are used, one is placed in the middle of the track and two are placed outside the track. When the car is out of the track, that is, when one photoelectric switch placed in the middle is out of the track, wait for any one outside to detect the black line, and then make corresponding steering adjustment until the photoelectric switch in the middle detects the black line again (i.e. returns to the track), and then resume forward driving. The field measurement shows that the trolley has a certain swing in the process of tracking. Although it can track correctly, its cost and stability are second to the second scheme.Through comparison, I choose the second scheme to achieve tracking.