Abstract: Pollution prevention and control is an important issue facing developing countries. Finding and evaluating effective environmental protection policies is the focus of environmental economics. This paper uses the difference-in-difference method to identify the overall impact and mechanism of the first round of the Central Environmental Protection Inspections(CEPI) in China. We find that the first round of CEPI led to significant improvements in AQI, PM2.5, PM10 and SO₂ in the inspected cities, but there were no significant changes in CO, NO₂ and O₃. CEPI functions through two mechanisms: bottom-up public attention and top-down environmental law enforcement.