Most ventilation models do not consider the influences of furniture and obstacles on building ventilation. This study developed a resistance model to calculate the ventilation rate of wind-driven cross ventilation in a low-rise building with vertical plates in the building. The flow resistances generated by the plates of various sizes were systemically investigated using a Large Eddy Simulation model and wind tunnel experiments. The numerical and experimental results consistently demonstrated that the resistance factor is a function of the internal blockage ratio (ratio of the plate area to the internal cross-section area) and location, but is independent of the external wind speed, building size and opening configuration. It was also found that when the wall porosity is less 3%, the resistances caused by the external openings will dominate the ventilation process and the influence of the internal obstacles on the ventilation rate can be neglected. But when the internal resistance is larger than the external resistances, the diminish effect of the obstacles on the ventilation rate should be taken into account.