Construction Land Reduction (CLR) has emerged as a pivotal policy in China for optimizing land-use spatial structure, particularly in metropolitan suburbs. This study develops a novel "simulated reverse extrapolation" framework to quantify its effects, integrating the PLUS model with FRAGSTATS to assess CLR intensity and landscape patterns in Shanghai's suburbs. Our findings demonstrate that CLR significantly enhances landscape connectivity and curbs urban sprawl, mechanisms primarily driven by edge and agglomeration effects. These impacts, however, are heterogeneous, varying substantially with local land supply types, industrial development levels, and geographical context. Spatial econometric analysis of 96 suburban townships (2014–2024) confirms a significant spatial interdependence between CLR and land-use structure. The Spatial Durbin Model further reveals a nuanced spillover effect: while CLR robustly improves landscape connectivity within implementing towns, it generates negative externalities by reducing connectivity in adjacent areas. These insights provide critical empirical evidence for refining ecological civilization initiatives and optimizing territorial spatial planning.