The invention relates an optical projection system, which is used for imaging an image in an object plane to an image plane. A first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eight lens are successively arranged along an optical axis from an object side to an image side and a diaphragm is arranged between the fourth lens and the fifth lens. Besides, a back focus of a combined lens set including the first lens, the second lens, the third lens, and the fourth lens is in the center of the diaphragm; a front focus of a combined lens set including the fifth lens, the sixth lens, the seventh lens, and the eight lens is in the center of the diaphragm; therefore, a doubly telecentric structure is formed based on the above-mentioned arrangement. According to the optical projection system provided in the invention, if a technology factor is selected, wherein the technology factor is expressed as K1 being equal to 1.0 and is easily realized, a lithography resolution can completely reach 15 microns, so that a technical requirement of LDI lithography equipment of a PCB can be satisfied sufficiently; moreover, an optical material with high transmissivity is selected, so that an exposure requirement with large doses can be met.