The impact of inland large water bodies on the air environment of inland cities was investigated based on the method of CFD (Computational Fluid Dynamics) simulation with KRB coordinate transformation. Both urban heat island circulation and lake wind circulation were modelled by the CFD methodology, and they were verified by comparing with the reduced-scale water tank experiment. The urban island circulation was heavily influenced by the size of the water body and its distance to the urban center. It was shown that the larger the lake area, the greater offset of the observed urban thermal plume; whereas, when the distance from the city center to the water bodies increased, the offset of the heat island plume near the ground reduced. When the lake was located close to the city, lake-breeze and the city airflow put aiding effect, i.e., generating strong aiding circulations. However, as the lake was further away from the city, opposing effect was found between the lake wind and the urban heat island circulation. Cooperating aiding effect could be found between the diverging flow and lake wind beyond of the plume.