With the specific objective of exploring the surface pressure characteristics and further revealing the torsional vortex-induced vibration (VIV) mechanisms of a bridge deck with a particular geometry, numerous simultaneous pressure measurement campaigns were performed in a wind tunnel for aerodynamic-countermeasure-modified and unmodified sections of a section model at different angles of incidence under the conditions of smooth or turbulent flow. The mean and fluctuating pressure distributions, instantaneous pressures at typical instants, dominant pressure frequencies, pressure phase differences at the dominant frequency of individual pressure measurement taps, and the correlation coefficients among local and global torsional moments were studied, revealing the origins and mechanisms of torsional VIVs. The results demonstrate that the angle of incidence, flow conditions (smooth or turbulent), and installation of a spoiler exert significant effects on the surface pressure distributions, hence affecting the corresponding aerodynamic performance of the bridge deck. Turbulence on the top surface can potentially neutralize the vortex shedding effects and enhance immunity to torsional VIVs. The signature turbulence from the leading (fairing) edge was effectively weakened or even destroyed by sufficiently intense oncoming turbulence and/or the turbulence generated by a spoiler with an appropriate configuration and location. Therefore, potential torsional VIVs could be suppressed by the interaction of vortices generated by oncoming and signature turbulences. This knowledge is essential for a thorough evaluation of the potential for torsional VIVs for this particular bridge deck.