Abstract: It is introduced an critical potential safety hazard of a tower crane for project during lifting operation in Shenzhen.It is the derailment of the lifting hoop frame's guide wheel,which made the upper structure of the tower crane incline that caused the accident;then emergency treatments of raising,tying,strengthening and dismantling were conducted to resolve the accident effectively and timely.In the end,the causes of the accident and precautionary measures for similar incidents are analyzed and summarized.