Abstract: To address the challenge of controlling assembly accuracy due to the coupled transmission of multiple errors in multi-panel synthetic aperture radar (SAR) antenna deployment mechanisms, a modular error modeling approach was proposed. The complex deployment structure was decomposed into functional modules—hinges, rods, and panels—based on series-parallel mechanism principles. Parametric assembly error models for each module were established using the closed-loop vector method. By linearly superimposing the error-transfer functions of the modules, the pose errors of the antenna panels were mapped to global geometric-tolerance sources, enabling the prediction of geometric accuracy in statically indeterminate rod systems. Partial differential methods were further employed to quantify the sensitivity coefficients of individual error sources. Assembly and adjustment tests on a 22 m × 3 m antenna yielded a pointing accuracy better than 0.012°. The results demonstrate that the method provides a systematic theoretical tool for the digital assembly, adjustment, and tolerance optimization of SAR antennas, effectively enhancing on-orbit deployment accuracy and imaging performance.