The use of Double Skin Façade (DSF) has increased during the last decade. There are many reasons for this including e.g. aesthetics, sound insulation, improved indoor environment and energy savings. However, the influence on the indoor environment and energy consumption are very difficult to predict. This is manly due to the very transient and complex air flow in the naturally ventilated double skin façade cavity. In this paper the modelling of the DSF using a thermal simulation program, BSim, is discussed. The simulations are based on the measured weather boundary conditions, and the simulation results are compared to the measurement results like energy consumption for cooling, air temperature, temperature gradient and mass flow rate in the DSF cavity, etc. Details about the measurements are reported in \Kalyanova et al. 2008\. The thermal simulation program does not at the moment include a special model to simulate the DSF. However, the results show that it was possible to predict the energy flow, temperature distribution and airflow in the DSF. The good agreement between the measured and simulated results was unfortunately very sensitive to the model. This implies that without the possibility to calibrate the simulation model with measured data the risk of generating poor results is imminent. Therefore further work including both measurements and more detailed and robust simulation programs are necessary.