Aiming at spanwise correlation of vortex-induced forces (VIFs) of the main deck of bridges, wind tunnel experimens of an oscillating and stationary streamlined box girder were conducted under different wind attack angles in the smooth flow. The VIV responses, spanwise correlation of vortex-excited forces, and surface pressures of the streamlined box girder were investigated. The research results showed that the spanwise correlation coefficients of the vortex-excited forces of the streamlined box girder were related to the amplitudes and wind speeds in the lock-in region. The spanwise correlation coefficients of the vortex-excited forces of the main deck at ascending stage of the lock-in region were larger than that of the main deck at the maximum amplitude of the lock-in region. The spanwise correlation coefficients of the pitch moments of the main deck in torsional VIV were larger than that of the lift forces of the main deck in vertical VIV. Meanwhile, the spanwise correlation coefficients of the pressures on measure points of the main deck were related to the amplitudes of the oscillating main deck, and the spanwise correlation coefficients increased with the increase of the amplitudes.