1. A lane departure warning method for a vehicle, comprising: providing a drive video; generating an identification result of recognizing a plurality of lane lines according the drive video, wherein the identification result is generated based on inside borderlines of the lane lines, comprising: generating a processed drive video which includes a plurality of objects; determining a video central axis of the processed drive video; selecting a plurality of candidate lane line segments from the objects according to the video central axis, comprising: when there is no other object between an inside borderline of a specific object of the objects and the video central axis, determining the specific object is one of the candidate lane line segments; and generating the identification result according to the plurality of candidate lane line segments; determining a lane whereon the vehicle is traveling according to the identification result; determining a sensitivity of lane departure warning according to a speed at which the vehicle is traveling; and determining whether to issue a warning according to the determined lane and the sensitivity.