In recent years, the problem of global warming caused by the massive emission of carbon dioxide has attracted the attention of all countries in the world. As the world's largest carbon dioxide emitter. China is under great pressure to conserve energy and reduce emissions. How to effectively control carbon dioxide emissions has become one of the important issues that needs to be solved in China's economic and social development. The digital economy is characterized by technological innovation, environmental friendliness and green development providing new opportunities for carbon emission reduction. However, the existing literature has not reached a consensus on the study of the impact of China's digital economy development on carbon emissions, and the study of the internal mechanism of China's digital economy development on carbon emissions is not deep enough, and the study of the spatial spillover effect of China's digital economy development on carbon emissions is relatively few. Based on the extended Cobb-Douglas production function, this paper analyzes the impact of digital economy development on carbon emissions by using Chinese urban panel data. The results show that the development of the digital economy can significantly reduce the level of carbon emissions, and this result is still valid after a series of robustness tests. In terms of its mechanism, digital economy can reduce carbon emissions by strengthening environmental regulation, improving human capital level and promoting industrial agglomeration. After further considering the spatial correlation characteristics of the emission reduction effect of digital economy, it is found that the development of digital economy can not only promote carbon emission reduction in the region, but also help reduce carbon emissions in neighboring regions. Heterogeneity test shows that the development of digital economy significantly reduces carbon emissions in central cities and high-innovation cities, but the carbon emission reduction effect of digital economy in peripheral cities is not significant, and the development of digital economy in low- innovation cities significantly increases carbon emissions. The development of digital economy in eastern and central and western cities has significantly reduced carbon emissions, and the carbon emission reduction effect is decreasing from the central and western regions to the eastern regions. The possible marginal contributions of this paper are as follows: first, a theoretical model is built to analyze and empirically test the impact of digital economy on carbon emission by incorporating digital elements into Cobb-Douglas production function and introducing carbon emission equation, which deepens the understanding of the relationship between digital economy development and carbon emission. Second, three intermediary variables, i. e. industrial agglomeration, environmental regulation and human capital are included, which enriches the mechanism of the impact of digital economy development on carbon emissions from a new perspective based on multiple paths. A multidimensional index evaluation system is constructed to measure intermediary variables, which can reflect the characteristics of intermediary variables more completely and comprehensively than a single indicator measurement. Third, two spatial weight matrices of adjacency and inverse distance were constructed, and bidirectional fixed effect spatial Durbin model was adopted to test the spatial spillover effect of digital economy development on carbon emissions from a more subtle urban scale. Three intermediary variables of industrial agglomeration, environmental regulation and human capital were included in the model successively, and the spatial spillover effect of different intermediary variables on carbon emissions was investigated. It provides an empirical basis for the national planning of carbon emission reduction policies. The research in this paper deepens the understanding of the relationship between digital economy development and carbon emission to a certain extent, reveals the internal logic of China's digital economy development affecting carbon emission, clarifies the path and method of carbon emission reduction, and provides theoretical support for government departments to formulate more targeted policies on digital economy development and carbon emission reduction under the constraint of "dual carbon" goal. This will help promote the development of digital economy and carbon emission reduction, and better achieve China's carbon emission reduction targets. [ABSTRACT FROM AUTHOR]