While applications need to be synchronized with the long-term stable state of structure, so to be able with the pulley has been showing a very good assembly effect, in order to ensure that equipment is stable and reliable transmission, always keep a stable running effect. But due to the installation position and the relationship of the use, when the device is in use is still a certain change will happen. Synchronous belt in the use of changes, mainly appear length longer and more smooth surface changes of these two aspects. The length of these changes, because of the device in use, assembled with pulleys need to continue to run at a high speed. So will inevitably in long-term operation of belt wheel, a certain external force effects on the device, the longer it will change the length of the synchronous belt, will appear in length variable-length case is loose. As for the change of the synchronous belt on the surface state, because its in use need to be continually cooperate do tell the functioning of the pulley, which will have long belt wheel friction, friction and is told. Used in such cases, a long belt wheel surface will become smooth, longevity and synchronous belt may occur directly from the belt wheel slip on this kind of phenomenon. The length of the synchronous belt length, is becoming more and more smooth surface that is very normal phenomenon, the more serious the phenomenon that device damage more serious, change too obvious when often need to replace the new device.