AbstractReynolds stress turbulence models are still an effective method to solve thermal density flow in reservoir. Presently, these turbulence models have extensive research and play an important role in the project. However, the pursuit of a more general, economic and accurate Reynolds stress model is still necessary for buoyant turbulent flow. In this paper, an improved explicit algebraic Reynolds stress model was established accounting for buoyancy. The tensor representation of the Reynolds stresses are divided into two parts, the former is composed of EASM derived by Wallin & Johansson (2000) and latter is the formulations of buoyant stress. In the derivation of explicit algebraic active scalar flux model, WWJ (Wikström, Wallin and Johansson, 2000) model only for explicit tensor representation of passive scalar flux is improved by affiliating external buoyancy effects terms. The current EASM is discretized on three-dimensional unstructured grids and compared with experimental data of 3D thermal density flow. The calculations show that the model yields better results than LAHM and LARM. In addition, EASM model also has good stability and relative economic calculation CPU time-consuming. The current model would be promising in hydraulic engineering and environmental engineering.