The back of the polyurethane belt backing timing belt is used to bond and wrap the tensile element. It should have good flexibility and flex fatigue resistance, not easy to age, good oil resistance, and abrasion resistance, on the inner surface of the belt back A sharp-angled groove with an appropriate size can not only improve the flexural fatigue performance of the toothed belt due to process requirements, but also allow the intercepted air between the belt and the gear teeth to escape during operation to eliminate part of the noise.