The present disclosure discloses an optical imaging system, the optical imaging system having an effective focal length f and an entrance pupil diameter EPD, and comprising sequentially, along an optical axis from an object side to an image side, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens. The third lens has a negative refractive power; the fifth lens has a positive refractive power or a negative refractive power, and an image side surface of the fifth lens is a convex surface; the seventh lens has a positive refractive power or a negative refractive power, and an object side surface of the seventh lens is a concave surface; the first lens, the second lens, the fourth lens, and the sixth lens respectively have a positive refractive power or a negative refractive power.