Abstract: According to the computational fluid dynamics theory and the finite volume method, the governing equations of flow and heat transfer are solved for round horizontal thermal jets in flow. Using the Realizable k-ε turbulence model and the semi-implicit method for pressure linked equations-consistent algorithm and considering the buoyancy effect, a 3D numerical simulation of round horizontal thermal jets is achieved in this study. Both flow characteristics and temperature distributions in thermal jets are studied through the numerical experiments conducted under different conductions of velocity ratios and outlet temperatures, and the impact of these conductions on temperature distributions is analyzed. As a result, both velocity and temperature attenuation regularities of thermal jets are found. The study illustrates the practical value of numerical models for the examination of the discharge of thermal wastewater.