<p>Atmospheric turbulence distorts the complex wavefront of light in free-space optical communication systems, leading to bit errors and even communication interruptions. Recently, it is found that the non-separability of vectorial structured light remains invariant when transmitting through atmospheric turbulence. This discovery offers a potential solution for turbulence-resilient communications—encoding based on the non-separability of vectorial structured light. To achieve such turbulence-resilient communications, efficient detection of the non-separability of vectorial structured light is essential, which acts as the receivers of such communication systems. So far, traditional non-separability detection schemes usually rely on bulky SLMs or DMDs, facing inherent trade-offs between single-shot capability and system compactness. In addition, the detection of mode-resolved non-separability contributions of vectorial superposition states has not yet been accomplished. Here, we propose and experimentally demonstrate a coherent detector to characterize the non-separability of vectorial structured light based on off-axis digital holography, which overcomes the limitations of traditional approaches by digitally decomposing spatial modes. Our approach may pave the way for turbulence-resilient optical communications based on non-separability coding methods and bring new insights into non-separability measurement.</p>