In this paper, the wind flow mechanism of steel plate girder bridges is discussed based on computational fluid analysis. The analyis of steel plate girder bridges were carried out for the model which has four 3m height girders and its interval is 3m. As a result of analyis, the correspondance between experiment and analysis is confirmed, and it was observed that the distribution of drag coefficient is affected by the ratio of parapet and girder height, and it is found that the design method of lateral member is not necessarily safe side. The trial calculation of sway bracing based on the analysis were conducted. As a result of calculation the section of sway bracing needs to be changed from the one designed by the current design method.
