An optical lens system for taking image comprises, in order from the object side to the image side: a first lens element with positive refractive power having a convex object-side surface; an aperture stop; a second lens element with negative refractive power; a third lens element having a convex object-side surface; and a fourth lens element with negative refractive power having a concave object-side surface, an image-side surface of the fourth lens element being aspheric and formed with inflection points. A distance from the image-side surface of the fourth lens element to an image plane along an optical axis being BFL, a total track length of the optical lens system for taking image being TTL, and they satisfy the relation: BFL/TTL>0.12. In the optical lens system for taking image, the number of lens elements with refractive power being limited to four.