An optical imaging system including, sequentially from an object side to an image side along an optical axis, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens. The first lens and the third lens each has a positive refractive power. The second lens, the fourth lens, the fifth lens, the sixth lens, and the seventh lens each has a positive or a negative refractive power. An object-side surface of the first lens is convex, and an image-side surface thereof is concave. An image-side surface of the second lens is concave. An object-side surface of the third lens is convex. An object-side surface of the seventh lens is convex, and an image-side surface thereof is concave. A total effective focal length f of the system and an entrance pupil diameter EPD of the system satisfy: f/EPD≤1.5.