Abstract: The segmented solar telescope described in this study employs a simultaneous dual-wavelength measurement technique to achieve co-phase alignment. To meet the measurement requirements of a 20 μm range, 5 nm root mean square precision, and edge jump rates of < 10⁻⁶, this study focused on calibrating the dual-wavelength measurement system for the segmented-mirror solar telescope. Analysis of the relative error in the measurement system revealed that assembly-induced errors such as defocus, translation, scaling, and rotation markedly degrade measurement accuracy. To address these issues, we propose a defocus error compensation algorithm, based on the light intensity distribution of the point spread function (PSF) and an affine transformation model, to calibrate spatial pose deviations across the two measurement channels. A dual-wavelength measurement system was implemented on a segmented-mirror experimental platform for calibration. Experimental results demonstrated that the mean relative error decreased from −0.6423 to −0.0345 nm after calibration, reflecting improved reliability and stability of the co-phase measurements.