A lens unit, a lens for a low-beam illumination module, a low-beam illumination module and a vehicle. The lens unit includes a rear surface and a front surface; the lens unit has a focal line, and the focal line is a straight line perpendicular to a light emitting direction of the lens unit; the rear surface and the front surface are adapted to project light rays passing through the focal line into parallel light rays, and the front surface is a free-form curved surface. The lens unit has the optical characteristics of a cylindrical lens, and is able to cause parallel incident light to be focused into a line instead of a focal point upon passing through the lens unit.