In the process of urbanization and industrialization in China, environmental pollution has always been one of the most concerned issues. In the report of the 19th National Congress of the Communist Party of China, General Secretary Xi Jinping emphasized that we should focus on key tasks such as the defense of the blue sky, continue to promote pollution prevention and control, strengthen the protection and restoration of ecosystems, expand green environmental protection industries, vigorously promote green development, and continue to improve the quality of the ecological environment. Compared with the serious "urban disease" caused by traffic pollutants in Chinese cities, high-speed rail (HSR) is one of the most sustainable green transportation infrastructures. This paper studies the impact of HSR on the environmental pollution and its mechanism by employing a spatial econometric model and an intermediary effect model with the panel data of 285 cities in 2010-2018. The empirical results show that: 1) The urban environmental pollution in China has significant spatial spillover effects, which means that environmental pollution control should follow the strategy of regional joint prevention and control. 2) HSR can reduce environmental pollution. Compared with cities without HSR, the annual average PM_2.5 concentration, nitrogen oxide emissions per unit of GDP, and industrial wastewater discharge per unit of GDP in HSR cities are reduced by 1.5%, 11.4%, and 12%, respectively. 3) HSR’s reduction effect on the environmental pollution is significant in the eastern and western regions, while that in non-central cities is greater than in central cities, indicating that HSR network can reduce the imbalance of urban ecological efficiency to a certain extent and contribute to the coordinated development of the environment. 4) HSR reduce the environmental pollution by increasing the total factor productivity. This paper provides a theoretical reference for realizing the inhibitory effect of HSR on urban environmental pollution, and provides the following policy references for the construction and development of HSR: 1) China’s high-speed rail is an important infrastructure that changes the spatial and geographical pattern of cities, and environmental pollution has significant spatial spillover effects. Therefore, the regional joint prevention and control strategies for environmental pollution should be considered from the perspective of urban spatial geography, especially considering academic discussions and policies. The effect of HSR network layout on environmental pollution, which is rarely discussed in practice, has important theoretical and practical value. 2) The opening of high-speed rail has a heterogeneous effect on restraining urban environmental pollution. Further promoting the construction of new transportation infrastructure in the central and western regions and non-central cities, and promoting the modernization and efficiency improvement of the intercity transportation network, will not only help the local economic development, but also be conducive to the protection of the ecological environment.