The invention discloses an optical imaging system. The optical imaging system sequentially comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a six lens along the optical axis from the object side to the image side, wherein the first lens has focal power, and the object side of the first lens is a convex face; the second lens has focal power; the third lens has focal power, and the image side of the third lens is a convex face; the fourth lens has focal power, the object side of the fourth lens is a convex face, and the image side of the fourth lens is a concave face; the fifth lens has positive focal power, and the object side of the fifth lens is a convex face; the sixth lens has negative focal power, and the object side of the sixth lens is a concave face. The maximum half field of view HFOV of the optical imaging system is larger than 50 degrees and smaller than 60 degrees, and the ratio of the curvature radius R7 of the fourth lens object side tothe total effective focal length f of the optical imaging system is larger than 0.4 and smaller than 1.5.