As　a　regional　green　industrial　policy,　the　construction　of　national　eco-industrial　parks　is　of　great　significance　to　the　realization　of　industrial　green　transformation,　while　its　environmental　effects　and　mechanisms　have　not　yet　been　clarified.　Using　panel　data　from　308　prefecture-level　cities　in　China　from　2003　to　2017,　this　study　takes　the　establishment　of　3　national-level　ecological　industrial　parks　as　a　quasi-natural　experiment,　also　using　a　time-varying　difference　in　difference　model　to　examine　how　green　industrial　policies　affect　industrial　pollution　emissions.　The　study　found　that　the　establishment　of　a　national　eco-industrial　park　has　significantly　reduced　industrial　sulfur　dioxide　emissions,　and　the　emission　reduction　effect　has　a　lag　effect　and　long-term　impact.　In　cities　with　strong　environmental　regulations,　provincial　capitals　and　municipalities,　and　cities　with　a　high　degree　of　marketization,　eco-industrial　parks　have　better　emission　reduction　effects,　while,　in　cities　with　greater　economic　growth　incentives　and　fiscal　pressures,　eco-industrial　parks　are　difficult　to　achieve　emission　reduction　effects.　The　establishment　of　national　eco-industrial　parks　can　reduce　industrial　pollution　emissions　by　improving　pollution　treatment　efficiency　and　energy　efficiency,　as　well　as　promoting　industrial　agglomeration.　China　should　continue　to　promote　the　implementation　of　green　industrial　policies,　to　strengthen　the　construction　of　national-level　eco-industrial　parks　at　this　stage.