With the rapid urbanization, the increasing crime is the main challenge of urban governance. As a new governance model, smart city aims to alleviate various urban diseases. However,can constructing a smart city reduce crime? There is no evidence for this. Based on the quasi natural experiment of smart city pilot policy launched in 2012 in China, this paper collects the paneldata of 292 prefecture level cities from 2005 to 2020, uses the staggered difference-in-difference modelto evaluate the effect of smart city on crime, and makes an in-depth discussion on its mechanism.The study found that: (1) Building a smart city can significantly reduce the number of crimes; (2)Smart city mainly exerts its influence on reducing crime through three mechanisms: Increase residents?? income, improve the application of technology and optimize the allocation of resources; (3) Heterogeneity analysis shows that cities of different sizes and levels of developmenthave different effects on crime reduction through the smart cities. This paper provides important policy enlightenment for improve the urban public security.