Studying the carbon process and clarifying the impact of energy on the carbon cycle, can provide a reference for the formulation and implementation of carbon emission reduction policies, especially in urban areas. In this study, we estimated the carbon storage and flux in Beijing from 2005 to 2014 based on the urban carbon cycle model and analysed the impact of energy on the urban carbon cycle using the energy carbon effect index. The results showed that the artificial carbon storage was the main driving force for the increase in the total carbon storage in Beijing. Horizontal input was the main carbon input in Beijing indicating that the development of Beijing strongly depended on the materials supplied from external environment. Vertical output was the main carbon output in Beijing in the form of energy consumption. The carbon flux related to energy activities accounted for the total carbon flux in Beijing, namely the carbon effect of energy, was as high as 79.46% in 2006, then the ratio began to show a trend of fluctuating decline. The greatest impact of energy on Beijing's carbon cycle was from a vertical output direction, followed by a horizontal input direction. Therefore, strengthening the regulation and management of vertical carbon flux and horizontal carbon flux would be needed for city construction to lower carbon emissions. At the same time, it is important for Beijing to protect natural vegetation and increase ecological land area to enhance the city's carbon emission reduction capacity.