Conventional optical time-domain reflectometry (OTDR) schemes for passive optical network (PON) link monitoring are limited by insufficient dynamic range and spatial resolution. The expansion of PONs, with increasing optical network units (ONUs) and cascaded splitters, imposes even more stringent demands on the dynamic range of monitoring systems. To address these challenges, we propose a time-gated digital optical frequency-domain reflectometry (TGD-OFDR) system for PON monitoring that effectively decouples the inherent coupling between spatial resolution and pulse width. The proposed system achieves both high spatial resolution (~0.3 m) and high dynamic range (~30 dB) simultaneously, marking a significant advancement in optical link monitoring.