The present disclosure discloses an optical imaging system including, sequentially from an object side to an image side along an optical axis, a first lens having negative refractive power with a convex object-side surface; a second lens having negative refractive power; a third lens having positive refractive power; a fourth lens having positive refractive power; a fifth lens having negative refractive power; and a sixth lens having positive refractive power. A maximum field-of-view FOV of the optical imaging system and a distance TTL along the optical axis from the object-side surface of the first lens to an imaging plane of the optical imaging system satisfy tan(FOV/2)/TTL>1.0 mm−1. A center thickness CT1 of the first lens along the optical axis and a center thickness CT4 of the fourth lens along the optical axis satisfy 0.9≤CT1/CT4