Reynolds numbers have great effects on the pressure distribution of large-span roof structure. To explore these issues, Large Eddy Simulation (LES) numerical method was adopted to calculate mean and fluctuation wind pressure distributions. The pressure values, flow separation and reattachment patterns were examined by corresponding experiment data. Results indicate that the pressure distribution changed dramatically with different Reynolds numbers. Pressure distribution keep srelatively stable in low Reynolds number flow field, while for high Reynolds number flow,pressure varies rapidly at the leading edge area of the roof and gradually decreases to a constant value. The simulation results prove that Reynolds numbers have critical effects on the pressure distribution of the large-span roof structures.