The welding seam of the upper tensilerods safety hangers of GQ70 light oiltank truck may split easily during the operation. But the safety hangers usually bear small load, and its failure is not a material strength problem. The modal test with hammering method is carried out at some key portions of the safety hangers. Using experimental modal analysis method, the modal frequencies of the hangers are found. Through comparative analysis, the cause of splitting of the hangers is found, and some suggestions for repairing are proposed.