According to the reasons and features of car accidents happening in vehicles’ side areas, this paper designed and developed a kind of automotive lateral anti-collision warning system by frequency modulation continuous wave, based on the research on 24GHz linear frequency modulation continuous wave radar-probing system. The system designed in this paper will forecast the potential danger to drivers and avoid the accidents. The hardware structures, algorithm, program flows and working patterns of the warning system were introduced. Furthermore, pointing to the problem of false alarms, a kind of filtering method was presented creatively. This method improved the reliability of the warning system and the accuracy of the forecast. It filtered the disturbance coming from the side of the vehicles, and solved the difficult problem that prevented the millimeter-wave radar from being applied in automotive lateral anti-collision warning system. Finally, the experiment was designed and carried out. The result verified the rationality of the solution and the practicality of the system’s function.