Compared with common single deck bridge, the cross section aerodynamic optimization of twin deck bridge girder is stricter because the aerodynamic performance of both forward girder and leeward girder should be good at the same time. Based on a twin deck bridge which is under construction, a serial of wind tunnel tests of the sectional models were performed to get the best girder cross section through aerodynamic optimization of basic shape of girder cross section, position and height of repair-vehicle rail. This start a preliminary study on cross section aerodynamic optimization of twin deck bridge girder.