An optical system, a camera module, and an electronic device are provided. The optical system includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power which are sequentially arranged from an object side to an image side along an optical axis of the optical system. The first lens group includes a first lens. The second lens group includes a second lens, a third lens, and a fourth lens. The third lens group includes a fifth lens, a sixth lens, a seventh lens, and an eighth lens. A distance between any two groups of the first lens group, the second lens group, and the third lens group is adjustable such that the optical system is operable to be at a telephoto end, an intermediate, and a wide-angle end.