In this project, numerical study of dispersion and rise of smoke plume and distribution of pollutant concentration on the ground level in 3-D and unsteady condition has been done. Also spread of plume with time and distance from stack has been investigated. Because of high temperature difference between smoke plume and environmental air, buoyancy force is considered. Atmospheric conditions are applied as temperature and velocity changes with altitude in wind flow entrance. Reaction between smoke plume and environmental air is ignored. The mesh has been smaller where there are intense concentration gradients. In order to reduce the calculation time and because of symmetrical geometry, the solution domain is halfed. In comparison between achieved results for smoke plume distribution from numerical solution and Gaussian model a few difference are seen which are caused by supposition that are used for achievement of Gaussian model. The results of smoke plume rise are compared with experience relations too, which have a good agreement with each other. Numerical simulation predicts the smoke plume rise just less than experience amounts. So the amount of pollution concentration on the ground level in numerical simulation just over than Gaussian model. The amount of smoke plume rise in stable and unstable atmosphere states is minimum and maximum ordinary. So pollution concentration in ground level in stable and unstable atmosphere states is maximum and minimum ordinary. Also values of the ground level concentration of air pollutants were evaluated as a function of wind speed in two cases. Results of ground level concentration in two conditions of wind speed show that in a light wind speed, maximum ground level is occurred in far away from stack rather than strong wind speed. In two conditions of wind speed rise of plume compared with together. Results show that in a light wind speed the plume will rise much more than in a strong wind. Consequently, the height of rise is a function of the wind speed and in particular is inversely proportional to the wind speed. Key Words Smoke plume simulation, Stack, Chimney, Atmospheric condition, Plume rise and dispersion, Ground level concentration.