In order to analyze the mechanism of the urban heat island, it is paramount and meaningful to estimate the anthropogenic heat flux in cities. A case study was carried out to study the energy balance process in Beijing, China, based on a canopy energy balance equation and to estimate the urban energy fluxes and anthropogenic heat discharge and their seasonal and spatial variations. Two ASTER images and meteorological observation data from the winter and summer seasons were used for the study. The results showed that: (1) in Beijing, the anthropogenic heat discharge flux reached a maximum of in winter and in summer. Spatially, the magnitude of the flux was significantly affected by urban land cover types. In winter, the highest value occurred at an urban commercial district with an average value of . In summer, the highest value occurred at the airport and the industrial areas with the regional average reaching ; the spatial pattern of the heat discharge appears to be clustered, with some, localized high-accumulation centers such as in industrial areas and commercial districts. (2) The anthropogenic discharge was one of the important contributors to the surface-atmosphere energy exchange in cities. The heat discharge had a positive effect on elevating the surface temperature and formation of the urban heat island, especially in the summer. The study confirms the importance to account for the impact of the anthropogenic heat flux on urban energy budget.