The invention provides a low-cost overtaking early warning system based on visual perception, relates to the field of active automobile safety, and aims at solving the problem that rear/lateral collision occurs in the overtaking process when a driver does not detect and evaluate the surrounding of lanes comprehensively or estimate the sight distance of overtaking properly. The system comprises a front detection module, a back detection module, an overtaking early warning system controller, a display and alarm unit and a speed sensor. Via the system, alarm is raised against a dangerous or potentially dangerous condition, so that traffic accidents can be avoided effectively, and a driver is prompted to overtake or return to an original lane safely if there is not potential danger, and the burden of the driver is alleviated; and a binocular visual sensor is used to obtain traffic information of front and back of the lane as well as that of adjacent lanes, and compares a laser radar scheme, the cost of the system is much lower.