Under the strategic background of constructing a new development paradigm and breaking through "bottleneck" technologies，the "specialized，refined，distinctive and innovative" （SRDI） policy，as a crucial measure to cultivate technology-based small giant enterprises，urgently requires scientific evaluation of its policy effects. Using a sample of Chinese listed companies from 1998 to 2022，this study systematically examined the impact of the SRDI policy on firms' total factor productivity （TFP） and its mechanisms through a multi-period difference-in-differences approach. The findings revealed that the SRDI policy significantly enhances enterprise TFP，with results remaining robust after addressing endogeneity concerns. Extended analyses demonstrated that the policy exerts dual effects on productivity growth—simultaneously operating through intensive margin （efficiency improvements） and extensive margin （scale expansion） channels. Heterogeneity analysis indicated concentrated policy effects within the industrial sector，validating its targeted support for key domains outlined in the Made in China 2025 strategy. Mechanism tests identified two transmission pathways:（1） crowding-in private R&D investment，and （2） extending supply chain linkages. This research empirically verifies the SRDI policy's positive role in fostering the growth of niche technology leaders，and will provide theoretical underpinnings and empirical evidence for optimizing industrial policy design and strengthening supply chain resilience.