In a stitching interference system, a near-zero light path is required to measure the sub-aperture face shape to minimize the effects of phase-measurement errors caused by mechanical vibrations, phase shift inaccuracies, and retrace errors on the measurement results. Therefore, a two-dimensional rotation stage based on a flexible hinge was designed to precisely adjust the measured mirror attitude. A modal analysis of the rotation stage was conducted via finite-element simulation, and the natural frequency was verified experimentally, which showed good consistency with the simulation. This rotation stage, whose angular resolution exceeds 50 nrad, was used to adjust the pitch and roll attitudes of the test mirror. The experimental results indicate good consistency between the adjustment angle of the rotation stage and the attitude change angle of the testing mirror measured using an interferometer. The measurement results of the stitching interference system matched those of the long-trace profiler for the large-aperture flat mirror. The constructed stitching interference system satisfies the preliminary measurement requirements.