Abstract: It is found out that the open joint of the longitudinal joint has increased to different extent after longitudinal joint grouting in the flood sluicing sections of the TGP dam. In this paper, the changes in the open joint of longitudinal joint are disposed and the results through three-dimension finite element method are analyzed. The emphasis is put to introduce the rules of open joint of longitudinal joint Ⅰ before and after grouting in the flood sluicing section, and elementary findings in the causes of the changes in the open joint of longitudinal joint, also introduces the influence on stress and deformation of the dam structure owing to the increment of open joint after grouting.?