The invention discloses a five-piece imaging lens group comprising a fixed diaphragm and an optical lens group. The optical lens group sequentially comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens along an optical axis. The first lens has negative refractive power near the optical axis, and the image-side optical surface thereof is concave. The second lens has negative refractive power near the optical axis. The third lens has positive refractive power near the optical axis, and both the object-side optical surface and the image-side optical surface thereof are convex. The fourth lens has positive refractive power near the optical axis, and the object-side optical surface thereof is convex. The fifth lens has negative refractive power near the optical axis, and the image-side optical surface thereof is convex. There is an air gap length between the image-side optical surface of the fourth lens and the object-side optical surface of the fifth lens.