The invention discloses an optical system, a lens module and electronic equipment. The optical system sequentially comprises a first lens to a fifth lens with refractive power from an object side to an image side along an optical axis,and a diaphragm between a second lens and a third lens, wherein the first lens and the fourth lens have negative refractive power, the second lens, the third lens and the fifth lens have positive refractive power, the object side surface of the first lens, the image side surface of the second lens and the mirror surfaces of the third lens and the fifth lens are convex at a paraxial region, the image side surface of the first lens, the object side surface of the second lens and the mirror surface of the fourth lens are concave at a paraxial region, the optical system satisfies the following relational expressions that f12 / f35 is more than -2.5 and less than -1.5, f12 is the effective combined focal length of the first lens and the second lens, and f35 is the effective combined focal length of the third lens and the fifth lens. According to the invention, the surface type and the refractive power of the lens are reasonably designed, and the relational expression is met, so that the imaging quality is improved while the optical system meets the wide-angle imaging range.