As the core force of high-quality small and medium-sized enterprises (SMEs), SSDN “little giants” not only have outstanding innovative capabilities, but also serve as leading firms that strengthen the overall industrial chain. This paper mainly focuses on SMEs listed on China’s NEEQ, takes the batch accreditation policy of “little giants” at the national level as a quasi-natural experiment, and employs a multi-period DID model to investigate the supply chain innovation spillover effect of the accreditation of “little giants”. The findings reveal that accreditation can significantly enhance the innovation strength of supply chain partners through the three mechanisms of resource effect, competition effect, and demonstration effect. Further analysis shows that the innovation spillover varies depending on the characteristics of supply chain entities and relationships. When the focal firm has weak substitutability, supply chain partners have strong absorptive capacity, and the supply chain exhibits high stability, high transaction intensity, and close geographical proximity, the innovation spillover effect of “little giants” is more pronounced. Additionally, the accreditation of “little giants” can also generate innovation spillovers to higher-tier supply chain partners. This paper captures the “great energy” released by SSDN “little giants” along the supply chain, which not only clarifies the transmission mechanism of innovation “positive externalities”, but also provides practical inspiration for the government to build a gradient cultivation system for SMEs.