The Gaussian plume model is widely used to calculate the concentration of gaseous radioactive effluents in the atmosphere. This model assumes that the terrain is flat, so that the dispersion coefficients which are the most important parameters in this model must be compensated in complex terrain such as in Korea. In this study the compensation of vertical dispersion coefficient in two dimensional X-Z plane has been accomplished by comparing the Gaussian plume model with numerical model. The results show that the concentrations of radioactive effluents over complex terrain are more diluted than those expected over flat terrain.