Enhancing firm total factor productivity (TFP) is critical for achieving high-quality economic development. As a key application of financial technology (FinTech) in the real economy, supply chain finance (SCF) remains underexplored in its internal mechanisms for TFP improvement. Existing studies primarily focus on technological progress, credit constraints, and inclusive finance, leaving a gap in understanding the role of SCF depth. Using panel data from Chinese A-share listed manufacturing firms (2012-2021), this study examines how FinTech development affects firm TFP from the perspective of core enterprises. The results indicate that: 1) FinTech significantly improves firm TFP; 2) The effect is heterogeneous across firm types, with resource-processing industries, local state-owned enterprises, and private firms benefiting more prominently; 3) SCF depth mediates this relationship by alleviating short-term funding pressures, enhancing liquidity, and optimizing financial structures on both supply and sales sides. These findings provide empirical evidence for policymakers and practitioners to leverage FinTech and SCF for productivity growth in China.