The invention relates to a four-sheet type imaging lens group. The four-sheet type imaging lens group comprises a fixed diaphragm and an optical group; the optical group comprises a first lens, a second lens, a third lens and a fourth lens; the first lens has positive refractive power adjacent to a center optical axis; a surface of the first lens, which faces an object side, is a convex surface; the second lens has positive refractive power adjacent to the center optical axis; a surface of the second lens, which faces an image side, is a convex surface; at least one surface of the second lens is an aspheric surface; the third lens has negative refractive power adjacent to the center optical axis; a surface of the third lens, which faces the image side, is a convex surface; at least one surface of the third lens is an aspheric surface; the fourth lens has refractive power adjacent to the center optical axis; a surface of the fourth lens, which faces the object side, is a convex surface; and a surface of the fourth lens, which faces the image side, is a concave surface; and at least one surface of the fourth lens has points of inflexion. The optical group satisfies the following conditions that: 2.520; and 1.0