Abstract: There exist aerodynamic interference effects between the windward deck and the leeward deck of twin-deck bridges under wind load. Aerodynamic interference effects on aerodynamic coefficients of a twin-deck bridge were investigated with a series of section-model wind tunnel tests using both force-measurement method and pressure-measurement method. The results show that the aerodynamic interference effects on drag coefficients of twin-deck bridges could not be neglected. Compared with single deck alone, the drag coefficients of leeward deck are much smaller and those of windward deck decrease slightly. The aerodynamic interference effects on the lift and torque coefficients of twin-deck bridge could be ignored.