The vortex resonance characteristics of one typical streamlined bridge girder are studied using surface pressure measuring technique. Based on the testing results in smooth and turbulent flows with different attack angles, the means, standard deviations, power spectra of fluctuated pressures, as well as the correlations between local and total aerodynamic forces are comprehensively analyzed, and the torsional vortex vibration mechanism is disclosed. The research results indicate that, for the vortex resonance case, the flow separation at upper and lower surfaces is more severe than that of non-vortex case. The upper surface pressure fluctuation at the middle and downstream region is most obvious, which is incurred by the flow separation at the upper surface upstream tip. At the middle and downstream region, the aerodynamic forces keep good correlations with the total forces, and they provide the major torsional moment for vortex resonance. Vortex vibration depends on both fluctuation intensity and peak location. For the vortex resonance case, the surface fluctuated pressures are locked in the same frequencies.