Some great earthquakes of magnitude 8 or greater on China mainland repeatedly occurred at the intervals of 252, 94, 48, and 25 years. It incited us to study the time interval between every pair of great earthquakes (M≥8) on China mainland. The result shows that there are four groups of clear orderliness distinguished in the most disorder distribution of earthquakes. The distinguished orderliness can be used to estimate the occurrence of next great earthquakes in China.