Abstract: Metal collapsible tube were founded to have discontinuous black spots at the interface along the axie. Macro and micro observation on the interface of bellows, energy spectrum analysis and infrared spectrum analysis were used to analysis the causes of black spots. At the same time, the actual technological process of the metal collapsible tube was under consideration. The results show that the black spots came from the lubricant of electric pump in the strength test. The lubricant mixed into the water in the process of strength test, attached to the interface of bellows when the water flowed from the tube, and then reacted with the air in the high-temperature environment of drying. It is proposed that the electric pump and water tank of strength tester should be kept apart, add air blowing in both ways of tube after the strength test and oil removal before the last drying are also necessary.