There are 439 sets of broken bolts and 16 073 sets of seriously corroded bolts on a bolted steel box girder with a main span of 618 m. The fracture reasons are analyzed from the aspects of initial material defects, processing technology, stress corrosion, mechanical properties and fatigue fracture by using the methods of disease investigation, metallographic analysis, chemical component analysis and finite element analysis. The results show that the bridge deck water seeps into the box girder from the connection joint at the pavement damage. The caused stress corrosion is the main reason to cause the fracture of the high-strength bolt of the bridge. Based on the analysis, the bolts with serious corrosion and fracture have to be replaced, and the seepage point is blocked, and the corrosion and fracture of high-strength bolt will be obviously reduced.