Under the background of carbon peaking and carbon neutrality, exploring the carbon emission reduction effect of urban ecological infrastructure is important for achieving sustainable development and modern development of cities. This article selected 214 prefecture level cities in China from 2003 to 2019 as samples. The entropy weight method was adopted to quantify the development level of urban ecological infrastructure development in China. A spatial econometric model was constructed to study the impact of urban ecological infrastructure development on carbon emissions and its spatial spillover effects. The research finds that:(1) By and large, the urban carbon emissions are on the rise, and the regions with high carbon emissions are cities with large population density, as well as the traditional industrial cities. The urban ecological infrastructure development level shows a trend of first decreasing and then increasing. High level cities are distributed in the eastern coastal areas, northwest cities, provincial capital cities in middle China, and municipalities directly under the central government. (2) The development of urban ecological infrastructure significantly promotes carbon emissions of local cities and neighboring cities, and this result passes the robustness test. Moreover, there is a lag in the carbon emission reduction effect of urban ecological infrastructure. Urban ecological infrastructure will have a significant carbon reduction effect after 12 years. (3) The development of urban secondary industry has an agglomeration effect, reducing the carbon emissions of neighboring cities. The higher the degree of opening to the outside world, the faster the flow of regional trade, which promotes the carbon emissions of neighboring cities. (4) Compared to other cities, the development of ecological infrastructure in the western cities, non-provincial capital cities, non-municipalities directly under the central government, and resource-based cities significantly promote urban carbon emissions. (5) In terms of policy development, on the one hand, efforts should be made to promote the development of urban ecological infrastructure and the transformation of the secondary industry, especially the construction of facilities such as urban greening facilities and garbage and wastewater treatment facilities. On the other hand, special attention should be paid to cities in the western region, non-provincial capital cities and non-municipalities directly under the central government, as well as resource-based cities. In order to stimulate these cities' momentum of ecological infrastructure construction and promote the realization of carbon peaking and carbon neutrality, the development of urban ecological infrastructure should be handled in the light of concrete circumstances.