The invention discloses a novel spherical absolute measurement system and a method thereof, wherein the system comprises a computer, a light source, a light splitting unit, a filter, a standard object lens, a measured spherical reflecting mirror, an electro-control translation stage and a data acquisition and transmission unit; the method comprises the steps of: at first, adjusting the confocal location of the measured spherical reflecting mirror on the standard object lens by the electro-control translation stage, controlling a Fizeau interferometer by the computer to perform surface detection on the measured spherical reflecting mirror once and then storing the detection data in the computer, then controlling the electro-control translation stage by the computer to enable the measured spherical reflecting mirror to generate, around the focal point, confocal shears of lambda y and lambda y in relation to an optical axis of the interferometer, and using the interferometer to perform two detections respectively and storing the detection data of the two detections in the computer, and separating the surface data of the measured spherical reflecting mirror from errors of system and reference surface by data processing software in the computer among the three detected surface data so as to obtain the absolute surface information of the measured optical mirror surface.