The present invention discloses a lane departure warning method, which functions to choose the data acquiring source according to brightness of the environment surrounding a vehicle and weather status so as to reduce the erroneous judgment of lane departure during image processing and analyzing. In addition, the present invention also presents a lane departure warning apparatus using the foregoing method, which comprises at least a first information acquisition unit, at least a second information acquisition and a information processing/information processing/controlling unit. The first information acquisition unit disposed on the vehicle is capable of capturing the image around the vehicle while the second information acquisition unit disposed on the bottom of the vehicle is capable of capturing image under the bottom of the vehicle. The image acquired from the first information acquisition unit and the second information acquisition unit is then sent to the processing and information processing/controlling unit for data processing.