Abstract: After 264 h working, an air pipe made of 1Cr18Ni9Ti in an aero engine cracked around brazing root zone. Through observating the macro/micro morphology of the fracture, analyzing the chemical composition of the air pipe, calculating the strength of the air pipe, the characteristics and causes of fracture were confirmed, and the improvement measure was given. The results show that the characterisitcs of the fracture of the air pipe was fatigue fracture and the fatigue extension stress was relatively small. The large assembly stress during assembly process was the main cause of the fatigue crack initiation. Improving assembly quality can effectively prevent the fracture of air tube.