Urban land surface models (ULSMs) are important tools for studying the climatic effects of human activity. Various kinds of ULSMs have been developed to simulate the land-atmosphere interactions in urban areas. Although the parameterization schemes of these models have become increasingly complicated, the influencing mechanisms and approaches of human-made land surface construction on urban land-atmosphere interactions still need further research. In this paper, some key parameters that are associated with urban land surface modeling were determined through a mechanistic study of the urban surface radiation budget and energy balance schemes in the integrated urban land model (IUM). These parameters are the surface albedo, three-dimensional fractional vegetation cover (FVC) and the correction factors for the net radiation absorption and surface roughness length. Then, these parameters were parameterized and optimized through a comparison with the observed flux data at the 325-m meteorology tower in downtown Beijing to improve the simulation ability of the IUM. The simulation results from the Noah land surface model coupled with the single-layer urban canopy model (Noah/SLUCM) were used and compared with the results from the IUM to demonstrate the better performance of the IUM model. The results indicate that after parameterizing and optimizing these key parameters, both the fluxes associated with the radiation budget and energy balance are substantially improved.