Based on the balanced panel data of 30 provinces in China from 2005 to 2019，a dynamic panel model was used to empirically test the mechanism and effect of environmental decentralization on the eco-efficiency of swine industry by clarifying the intrinsic mechanism of how environmental decentralization affects the eco-efficiency of swine industry. It is found that environmental decentralization significantly inhibits the improvement of eco-efficiency in the swine industry，and the results remain robust after overcoming the endogeneity problem by using two-stage least squares and conducting a series of tests.Mechanism tests show that environmental decentralization supresses the increase in environmental regulation intensity，leading to a negative effect on the eco-efficiency of the swine industry，with environmental regulation acting as a partial mediator effect between the two. Further analysis reveals that the decentralization of environmental administration significantly promotes the improvement of eco-efficiency in swine industry，while the decentralization of environmental supervision and environmental monitoring is detrimental to enhancing eco-efficiency in swine industry. In addition，the effect of environmental decentralization is also characterized by regional heterogeneity，with environmental decentralization promoting the eco-efficiency of swine industry in the eastern region and inhibiting it in the western region，while showing no significant impact in the central region. Therefore，the mechanism “black box” of environmental decentralization affecting the eco-efficiency of swine industry is explored，aiming to provide insights for the government to scientifically and reasonably allocate environmental management rights and responsibilities，formulate differentiated environmental decentralization strategies， and implement targeted policies.