This paper investigates how the Global Supply Chain Pressure Index (GSCPI) affects long-term stock–bond correlations in China, employing mixed-frequency data from April 2005 to June 2025 in a DCC-MIDAS-X framework. Results show that higher GSCPI significantly reduces long-term stock–bond correlations, thereby enhancing the hedging property of bonds. This effect is both state-dependent and asymmetric, remaining significant in low-volatility regimes and following negative shocks, while becoming largely muted during high-volatility periods or after positive shocks. However, the impact of GSCPI weakens substantially after China’s 2014 financial liberalization, as global financial factors increasingly drive cross-asset dynamics. Moreover, GSCPI provides incremental information that enhances portfolio diversification and hedging performance.