Abstract: In order to analyze quantitatively the effects of Center-Beam Approximation (CBA) on MOtion COmpensation (MOCO) for airborne Interferometric SAR (InSAR), a mathematical model of MOCO residual error under the condition of squint is firstly established. The form of residual error is similar to the slant range error. Then, the effects of quadratic slant range error on InSAR are deduced on condition that the squint angle is not zero, and the accuracy of the theoretical derivation is verified with simulation data. Finally, the effects of CBA on image quality and coherence coefficient for airborne InSAR are discussed in detail for different bands, squint angles, trajectory deviations, topography variation and slant ranges. The research provides technical support for the estimation of MOCO precision in signal processing of airborne repeat-pass interferometric SAR.