The invention discloses an optical four-lens unit for imaging, which comprises a first lens with positive refraction power, a second lens with negative refraction power, a crescent-shaped third lens with negative refraction power, and a fourth lens with negative fraction power which are disposed sequentially from the object side to the image side. The front surface of the first lens is a convex surface, the rear surface of the second lens is a concave face, at least one aspherical face is arranged on the second lens, the rear surface of the third lens is a convex surface, the front surface ofthe fourth lens is a convex surface, and the rear surface of the further lens is an aspherical face. With the lens structure, arrangement mode and lens configuration, the volume of the lens unit can be effectively reduced, and higher resolving power can be obtained.