Experiment and simulation were used to study the dispersion characteristics of heavy gas pollutants represented by carbon dioxide in isolated building terrain. Wind tunnel experiment and laser particle tracing technology were used to characterize the features of wind flow and the dispersion of pollutants. The influences of the distance from the building to the release source and the size of the building were explored. The results show that the height of the building has a significant effect on the wind speed and turbulence intensity on the windward and leeward sides of the building, and the side width of the building has a slightly weaker effect. The area of the recirculation region on the leeward side of the building and the barrier effect on pollutants are dominated by the windward area of the building, that is, the larger the windward area, the larger the recirculation region and the lower the concentration of pollutants on the leeward side. At the same time, the decline rate of pollutants on the windward side increases with the increase of the windward area. The heavy gas pollutants tend to spread around the building side with the wind flow, unless the distance from the building to the source is too short or the building is too long. And when the pollutants climb to the top of the building, the dispersion of them will slows down as the width of the building side increases. The RNG k-ε model was used for simulation to provide a visible result for wind flow, and its applicability and accuracy were verified.