Under certain load, the revolutions or hours of the bearing before pitting is known as the bearing life. In order to determine the standard of the bearing life, the bearing life is linked with the reliability. Due to differences of manufacturing accuracy and material uniformity, even for the same batch of bearings of the same material and size, in the same working conditions, the life length is not the same. If the statistical life is 1 unit, the longest relative life is 4 units, the shortest is 0.1-0.2 units. The ratio of the longest and shortest life is 20-40 times. 90% bearings do not produce pitting, revolutions or hours experienced is called the bearing rated life.