Ecosystem services (ESs) supply-demand balance is pivotal to understanding human-land interactions. However, it remains a core challenge to understand the effects of spatial mismatches on complex ESs interactions for ecological management. This study aims to systematically evaluate these interactions through an Integrated ESs supply-demand framework. Taking the Inner Mongolia grasslands as a model, we quantified the supply, demand, and balance of six key ESs for the 2000-2020 period. Through spatial clustering analysis, we identified ESs bundles and subsequently analyzed the trade-offs and synergies of ESs and their driving mechanisms within each bundle. Our analysis demonstrated a pronounced spatial-temporal heterogeneity and persistent regional imbalances in supply-demand of ESs in the region. While water yield supply declined, carbon sequestration and soil conservation improved. Although grassland carrying capacity and agricultural product output increased, regional disparities persist. ESs interactions exhibit pronounced bundle-specificity, influenced by internal variability within each bundle. The balances of carbon sequestration and food supply are trade-offs at the regional scale and within the central Inner Mongolia bundle, whereas they are synergistic within the water-scarce western bundle. Abiotic conditions dominate supply patterns, while human activities shape demand patterns, jointly shaping spatial-temporal ESs patterns including mismatches. The supply-demand spatial bundle provides operational perspective and precise management units for characterizing ESs interactions. Implementing management strategies targeting specific ESs bundles to mitigate critical trade-offs and enhance synergies offers a scientific pathway for the sustainable management of grassland socio-ecological systems.