A large eddy simulation(LES) program with the Smagorinsky subgrid-scale model has been used to study cross natural ventilation in buildings,which has esperimental data available from on-site measurements and a wind tunnel. since natural wind changes direction over time ,it is hard to reproduce this effect in a conventional wind tunnel where the "wind" direction is 8xed.There are discrepancies between the on-site and wind-tunel cases for the wind-pressure difference across the buildings ,the eddy size behind across wentilation.LES can successfully simulate both cases by changing or 8xing incoming wind direction,and the simulated results agree reasonably with the corresponding experimental data.