Effective air pollution abatement necessitates having a quantitative evaluation of the effect of environmental factors; wind velocities, temperature and topography on the movement of a pollutant. As a method evaluating synthetically for the environmental pollution, a simulator for air pollution has been developed, in which the system prints out a three dimensional pollutant concentration for each weather mode and for the distribution averaged over a long period, superimposes these results. The principle of simulating method for this system is described.