Abstract: Introduced ate the performance and characteristics of a kind of univetsal stretching joint made of double bellows. Actually structure is like this: one section of short pipe connected to two bellows on each end is linked internally by a rod. which makes it possible for the belows not to be stretching inspite of internal pressure. And the rod is able to swing in any direction within certain range of angles. This application has such a advantage that it can change the position in either ditection on the verticle line'therefore can serve as a pipeline compansator and also can be used as a connector of oil tank flexible pipes so as to avoide relative position change between tanks and piping when earthquake and foundation settlement take place. It is also pointed out that the side force of the stretching joint due to position change shall be taken as the design basis of pipeline hold- down supports. The writer also spends lines on the correlation between side force and internal pressure. In some publications abroad, some writers hold this opinion that the side force has nothing to do with internal pressure. some others think that they form a direct ratio. But tests and analysis show that the correlation pressure is rather complicated: if the friction force on the rod is low and side position change being very serious, the side force and internal pressure form an indirect ratio, otherwise, it could be on the contrary.