Abstract: The traditional method for measuring the right-angle error of a corner cube prism involves using the Fizeau interferometric system with a single-pass method. However, this method has some limitations, including the presence of systematic aberrations caused by multiple retro-reflections and errors introduced by adjusting the tilt of the reference mirror. An improved double-pass method was used to measure the right-angle error of a corner cube prism. This method could match the irregularities of the reference light and the test light, which eliminated the effect of systematic aberration and eliminated the need to adjust the reference mirror. Experiments were carried out using a Fizeau interferometer to measure the same corner cube prism using the traditional method and the improved method. Single-pass measurements result in dihedral angle errors of 0.978 5 μrad, 1.536 8 μrad, and −0.355 8 μrad, respectively. Double-pass measurements result in dihedral angle errors of 0.638 3 μrad, 1.260 9 μrad, and −0.311 3 μrad. The experimental results verify that the double-pass measurement method is more accurate than the single-pass measurement method.