Abstract: A certain amount of radioactive aerosols will be released into the atmosphere during normal operation of a nuclear power plant or in the presence of a nuclear accident. It is of great significance to study the atmospheric dispersion characteristics of aerosols under complex underlying surface conditions for the accurate evaluation of the radiative effects of airborne effluents. Gaussian plume or puff models are widely used in the evaluation of atmospheric dispersion. The dispersion parameters in these models describe the strength of aerosol dispersion due to turbulent flow. However, it needs to be corrected for different terrains such as flat and hilly underlying surfaces. The wind tunnel experiments of aerosol atmospheric dispersion under the conditions of flat and hilly underlying surface with Class D stability were carried out. The high-resolution aerosol concentration in a vertical section was statistically analyzed using a dispersion parameter estimation method based on laser particle image measurement. The upper and lower boundaries and dispersion parameters of downwind plume were estimated according to Gaussian distribution. The difference between the dispersion parameters of the flat underlying surface and the GB/T 3840—91 standard value is less than two times, which verifies the effectiveness of the method used. The plume trajectory of the hilly underlying surface condition indicates that the plume passes through the mountain and there is an overall elevation of the plume, which will lead to a decrease in the concentration near the surface after the mountain. In addition, there is an uneven distribution of concentrations on both sides of the concentration centerline before and after the plume passes through the mountain. The dispersion parameter in the part above the centerline reaches its maximum value at the windward slope. At the same time, the dispersion parameter in the part below the centerline reaches the minimum value at the top of the mountain. The plume trajectory returns to a Gaussian-like distribution after moving away from the mountain. The trajectories of the plume released from the source at 1/4, 1/2 and 1 times the height of the mountain show that the plumes released at less than 1/2 the height of the mountain are blocked and lifted by the mountain, and the trajectories tend to be consistent. For the plume releases above 1/2 height of the mountain, the plume trajectory increases as the release height rises. The dispersion concentration distribution of plume in hilly underlying surface is beyond the applicability of Gaussian model.