Abstract: A large-aperture Twyman–Green dynamic interferometer employs a high-precision primary mirror as its core component. Projection distortion between measured wavefront and actual surface figure of the mirror must be corrected to ensure the accuracy and efficiency of primary mirror’s compensation fabrication. To address issues of cumbersome and complex distortion correction methods that often neglect influence of internal optical path of interferometer, a correction method combining affine transformation and radial distortion modeling was proposed. Using a small number of targets and a coordinate measuring machine (CMM), an affine model was established. Through secondary programming development based on interface of optical design software, large-scale ray tracing and radial distortion fitting were performed to reconstruct interferometric wavefront distribution quickly and accurately. A decoupling method between alignment errors and surface figure errors after distortion correction was also analyzed. The proposed method was applied to correct projection distortion in compensation test results of an aspheric primary mirror with an effective aperture of Φ450 mm. Based on corrected results, magnetorheological finishing compensation of primary mirror was guided. The interferometric cavity wavefront root mean square (RMS) converged from 0.1093λ to 0.0104λ, which decreased by 90.48%, outperformed the convergence ratio achieved without distortion correction. Experimental results validate the effectiveness of the proposed method.