Abstract: The vortex-induced vibration (VIV) is a common form of wind-induced vibration of long span streamlined box-girder bridge under low wind speed. It has a great influence on the fatigue life and driving comfort of a bridge structure. In order to reveal the VIV mechanism of a streamlined box girder, it is necessary to study the aerodynamic evolution law of VIV of a streamlined box girder. Taking a streamlined box-girder bridge as an example, a wind tunnel test was conducted to obtain the VIV response and pressure time-history data from pressure measurement points on the experimental model for the angles of attack +5°. The changes of mean values of wind pressure coefficient, of root-mean-square (RMS) values of wind pressure coefficients and, of vortex-induced force (VIF) amplitude spectrum in different vortex-induced stages are analyzed. Those stages include pre-VIV stage, ascent stage, extreme amplitude point, descent stage, and post-VIV stage. It is found that mean values of wind pressure coefficients have little change, however, the distribution of RMS values of wind pressure coefficients has obvious changes. The VIF has obvious predominant frequencies in the ascent stage, at the extreme amplitude point, and in the descent stage. These frequencies are similar to the natural vibration frequency of the structure. However, there is no considerable predominant frequency in pre-VIV stage and post-VIV stage. The amplitude corresponding to the dominant frequency of VIF is positively correlated with the amplitude of VIV and reaches the maximum at the extreme amplitude point.