The piping safe end of regulator composed by a low alloy Inconel-600 material will appear leakage trend with long time running, so it is necessary to take an advanced welding repair. The purpose of this paper is to study the welding effect on piping vibration characteristics connected with the safe end of regulators, to provide the basis for welding piping safety assessment. Two different finite element modes that before and after welding of wave tube connected with the safe end of nuclear regulator are built by ANSYS program. The vibration characteristics of the different modes is discussed. The results show that little change of the vibration is happen when pressurizer pipeline system before and after welded repair . The evaluation criterion of the original stress analysis of the wave pipe system is also applied to evaluate its stress when the pipeline system welded repair.