Urban digital autonomy refers to the autonomous innovation capability of cities in the field of digital technology, which directly determines whether cities can achieve high-quality development in the urban digital economy. Using Chinese prefecture-level data from 2009 to 2018, this paper takes the smart city policy as a quasi-natural experiment to analyze the impact of the smart city policy on digital autonomy of cities empirically. The research results show that the smart city policy has significantly improved the digital autonomy of cities, which is 28.25% higher than that of other cities. After a series of robustness tests, such as the placebo test and propensity score matching DID (PSM-DID) test and using different samples, this research conclusion still holds. Heterogeneity shows that the promotion effect of the smart city policy on digital autonomy of cities is greater in eastern regions, cities with higher rank and larger population size. The research of influence mechanism shows that the smart city policy can promote digital autonomy of cities through the effect of digital human capital and digital material capital. Finally, this paper puts forward policy suggestions from the perspectives of developing digital industries, promoting the construction of smart cities, increasing the cultivation of digital talents, and paying attention to fairness and efficiency, so as to promote the digital autonomy of cities.