A numerical simulation has been made of the wind-driven ventilation in buildings with multiple windows and doors by adopting the method of computational fluid dynamics. First, the reliability of the computational fluid dynamics program can be fully verified by checking the calculated results against the classical experimental results. Then, a depth analysis and final calculation have been made of the different opening conditions of the cross flow ventilation, followed by a further study of the physical mechanism of the indoor air-flow. Finally, an analysis has been made of the results under discussion which mainly include the following factors: the velocity vector, velocity magnitude, velocity component, pressure distribution, and pressure coefficient, followed by a tentative study on the influence of incoming wind speed on the air flow field inside the building. The simulation results show that, when there is a side vent in the construction cross flow ventilation, the outlet of the leeward side may be used as an air intake.