The aperture in a spatial-carrier digital speckle pattern interferometry（SC-DSPI）system is a critical component determining its measurement performance. However, the specific impact of the aperture’s axial position remains underexplored. This study combines optical Fourier transform theory and experimental validation to analyze the influence of aperture axial displacement on spatial spectra and phase maps. Results indicate that altering the aperture position leads to spatial spectral loss, thereby degrading phase map quality. A trade-off exists between structural similarity（SSIM）and noise variance. Experimental optimization reveals that an intermediate position（65 mm）achieves a balanced improvement（SSIM 0.931, noise variance 3.82）, significantly enhancing phase map quality. This study provides important theoretical and practical guidance for optical path design and performance optimization in SC-DSPI systems.