With the deep integration of digitalization into urban development，it is crucial to systematically investigate the intricate relationship and underlying mechanisms between big data strategies and the advancement of new quality productive forces in cities to fully unleash their potential. Leveraging the quasi-natural experiment of national big data comprehensive pilot zone，this study employed the panel data from 277 prefecture-level cities spanning from 2009 to 2021 and adopted the difference-in-differences （DID） model to rigorously examine the impact of big data strategies on urban new quality productive forces and their underlying mechanisms. The findings revealed that the big data strategies significantly enhance new quality productive forces，with pronounced regional heterogeneity and temporal variation in policy effects. Specifically，the policy exhibits stronger promotional effects in eastern China compared to the central and western regions，and its impact is more substantial in early-policy-adopting cities than in late-policy-adopting cities. Through mediation analysis，we identified knowledge spillovers as the dominant mediating channel by which big data strategies contribute to the advancement of new quality productive forces. Further spatial econometric analysis confirmed a distinct spatial spillover effect. These conclusions will provide actionable insights for cultivating and developing new quality productive forces，while offering empirical support for advancing China's big data strategy to achieve the goals of "Digital China" and "Data Powerhouse".