Due to the different situations, importance and damage to personal safety and production losses caused by different size, ease maintenance and of gear reducer reliability requirements are not the same. Coefficient KR is a practical way to modify the original design of the reliability of reliability. It conforms to ISO6336, GB3480, and AGMA2001-B88 (United States gear Manufacturers Association standards) rules on calculation method for gear. Some users on the reliability of the gearbox is offered no specific requirements, as stipulated in the special gearbox design (SH = 1.25, failure probability = 1/1000), the more important occasions taken around KR=1.25=1.56.