The invention provides a tactical spotting scope optical system with a reticle-based ranging function, which is characterized in that a first lens of an objective lens, a second lens of the objective lens, a focusing lens of the objective lens, a Porro prism I, a Porro prism II, a reticle, a first compensation lens, a second compensation lens, a zoom lens I, a zoom lens II, a zoom lens III, a first lens of an eyepiece, a second lens of the eyepiece and a third lens of the eyepiece are sequentially arranged along an optical path; the focusing lens of the objective lens is a meniscus lens, the focal plane of the objective lens coincides with a first focal plane of the zoom eyepiece, and the dense ranging reticle is arranged at the coincidence position; the zoom lens I is a biconvex lens, the zoom lens II is a biconcave lens, and the convex surface of the zoom lens III faces the pupil; and the convex surface of the first lens of the eyepiece faces the pupil, the second lens of the eyepiece is a biconvex cemented lens, and the convex surface of the third lens of the eyepiece faces the object space. The focal plane of the objective lens and the first focal plane of the zoom eyepiece coincide with each other, and the reticle is arranged at the coincidence position, so that accurate ranging can be performed on an observed target by using the reticle in the whole zooming process.