Incorporating geopolitical interaction effects for a more comprehensive assessment of China’s border territorial functions

China possesses the world’s longest land border and one of its most intricate geopolitical environments. Previous research, however, has frequently overlooked the distinct geopolitical characteristics inherent to border areas, thereby constraining a comprehensive assessment of their functional systems, particularly concerning the effective integration of “Openness” and “Security.” This investigation amalgamates Endogenous Support Functions with Geopolitical Interaction Functions to systematically appraise the spatiotemporal dynamics, Coupling Coordination Degree (CCD), and, using the Optimal Parameters-based Geographical Detector (OPGD) model, the driving mechanisms of five-dimensional Border Territorial Functions across 45 of China’s Land Border Regions between 2005 and 2022. The findings reveal that the External Openness Function and National Security Function, which reflect Geopolitical Interaction Effects, underwent substantial growth, emerging as pivotal drivers of border functional evolution. Nevertheless, considerable variations persist in overall functional levels and amongst different regions. Whilst the CCD amongst these five functions has shown improvement, the overall level of coordination remains somewhat modest (for instance, rising significantly to 0.43 in the Southwest Border Region, yet remaining low at approximately 0.21 in the Tibet Border Region) owing to the complexities of multi-system coupling. This suggests that achieving a high degree of synergy amongst these multifaceted functions within China’s Land Border Regions continues to present a considerable challenge. In terms of driving mechanisms identified by the OPGD, natural endowments primarily mould the Ecological Protection Function and Agricultural Production Function; socio-economic factors propel the Urban Development Function and External Openness Function; whilst geopolitical and cross-border factors profoundly influence both the National Security Function and the External Openness Function. This study contends that Geopolitical Interaction Functions ought to be regarded as a critical constituent in the assessment of Border Territorial Functions, and that the synergistic development of these manifold functions is paramount for fostering stability and prosperity in China’s frontier regions. The research furnishes a novel theoretical perspective alongside empirical evidence for understanding and optimising complex border systems.