This paper presents a method for large-range， high-precision， and automated co-phasing alignment of segmented space telescopes. The approach satisfies the demands of millimeter-level range， nanometer-level precision， and operation without reliance on external interferometric measurement devices. Initially， the optical characteristics at various co-phasing stages-confocal alignment， coarse co-phasing， and fine co-phasing-are analyzed. Enhancements are made to the confocal alignment method， a coarse co-phasing detection technique based on a dispersion fringe sensor is developed， and a fine co-phasing detection method employing phase diversity is introduced. These advancements establish a comprehensive accuracy convergence chain for segmented mirror co-phasing alignment. Subsequently， an experimental system is constructed to validate the automated processes of confocal alignment， coarse co-phasing， and fine co-phasing. Experimental results demonstrate that when the relative position and orientation errors of sub-mirrors lie within ±0.5 mm and ±0.1°， respectively， the proposed method successfully achieves automated co-phasing. Following co-phasing， the system attains a wavefront error RMS better than 0.1λ（λ=632.8 nm）. The proposed co-phasing method provides a broad alignment range， high accuracy， and low resource consumption， rendering it highly promising for applications in segmented space telescopes.