Context <p>Urban green belts (UGBs) are large and continuous green infrastructure of cities. Owing to their spatial extent and continuity, they have the potential to exert broad influences on the urban thermal environment. Although most existing studies have focused on the cooling effects of scattered urban green spaces, the thermal environmental benefits provided by the extensive landscape structures of UGBs remain insufficiently understood.</p> Objectives <p>Taking Shanghai as an example, this study examines the impacts of UGBs on the urban thermal environment.</p> Methods <p>Morphological spatial pattern analysis (MSPA) and spatial statistical methods were employed to reveal how the Shanghai urban green belt (SHUGB) shapes urban heat island (HI) and cold island (CI) morphologies. Additionally, eXtreme Gradient Boosting (XGBoost) combined with Shapley Additive exPlanations (SHAP) was used to quantify the relationships between SHUGB landscape patterns and land surface temperature (LST).</p> Results <p>SHUGB separates urban-suburban HI cores while generating pronounced CI effects. Impervious surface percentage (imp_pland) was the most significant factor increasing LST, while higher vegetation and water body density contributed to cooling. Clear landscape pattern thresholds were identified, such as an imp_pland beyond 51.92% leading to significant warming.</p> Conclusions <p>This study demonstrates that UGBs can effectively disrupt the connectivity of HIs at the city scale. Concurrently, it underscores the critical importance of appropriate landscape design within UGBs for enhancing their cooling performance. Optimization strategies informed by the spatial patterns of HI/CIs and evidence-based landscape thresholds enable more targeted and efficient improvements in thermal mitigation.</p>