Environmental problems caused by fossil fuel consumption, on the one hand, and the upcoming prospect of ending these fuels on the other, attracted much attention towards sustainable architecture. Traditional buildings can be seen as a sample of sustainability; as they have used strategies to cope with the environment, which have been developed over the years, providing users’ comfort conditions for centuries. But before implementing these strategies in today buildings, we need to know the exact effect of their use; something that is regularly performed by an energy simulation software. Thus, first, we should know the ability of the software in modeling different design strategies, and secondly we should be certain of the validation of its results. This research aims to study the ability of Designbuilder software (as one of the most applied software for building energy simulation) to model and simulate a complex traditional building. The accuracy of Designbuilder thermal simulation results, in comparison with the experimental data is the main question of this study. To do this, Rasoulian house in Yazd (in hot and arid climate of Iran) was chosen as a case study and after simulating the entire building, the simulation results were compared with experimental measurement data. The results show that in most spaces, the experimental data were only 1– 5° C different from the results of the simulation. Finally, the probable causes of these differences were analyzed and some suggestions were proposed to develop Designbuilder, to be more applicable in simulating buildings of hot and arid climate.