Optical alignment of the mirror components in a space telescope is an important process for obtaining high optical resolution and performance of the camera system. The alignment of mirrors depends on the external coordinate frame using a cube mirror, and a relative coordinate mapping between the mirror and the cube mirror before optical system integration is a prerequisite step. Therefore, in order to align the spacecraft camera mirrors, the relative coordinates of the vertex of each mirror and the corresponding cube mirror must be accurately measured. This paper proposes a new method for finding the vertex position of a primary mirror by using an optical fiber and alignment segments of the computer-generated hologram (CGH). The measurement system is composed of an optical testing interferometer, a multimode optical fiber. We used 2 theodolites to measure the relative coordinates of the optical fiber located at the mirror vertex with respect to the cube mirror, and achieved a measurement precision of less than 25um.