The invention belongs to the technical field of the active forewarning of a running vehicle. The invention discloses a lane departure forewarning device and method for a vehicle on a highway under adverse weather, wherein the lane departure forewarning device comprises two multi-line laser radar sensors, a vehicle-mounted industrial personnel computer and a flashing buzzer; the two multi-line laser radar sensors are respectively mounted at symmetrical positions of the left side and the right side of a front bumper of the vehicle; the vehicle-mounted industrial personnel computer is mounted below an instrument panel of the vehicle; the flashing buzzer is mounted on the instrument panel of the vehicle; output ends of the two multi-line laser radar sensors are electrically connected with the I/O input ends of the vehicle-mounted industrial personnel computer, and the I/O output ends of the vehicle-mounted industrial personnel computer are connected with the input end of the flashing buzzer; whether the vehicle is in a lane departure state can be monitored in a real time manner without being influenced by weather conditions, a driver is prompted to take appropriate measures, the judgment burden of the driver is relieved and driving safety is improved.