The invention provides a method for preventing a key transport vehicle from overtaking illegally. A vehicle-mounted camera is used for carrying out image collecting on a road surface in front of the vehicle, whether a road marking line is a dotted line or a full line is obtained, a virtual safe zone is arranged on a video image in a view field collected by the camera, road marking lines on the two sides of a normally-running vehicle cannot enter the virtual safe zone arranged on the video image, when full lines enter the virtual safe zone and move all the way to the middle portion from one side, part of the vehicle passes over the full lines, and illegal line-crossing action is about to happen. Illegal line-crossing overtaking can easily cause traffic accidents, at the time, early warning is given out, a driver can realize the traffic offence, and the traffic offence can be corrected timely.