Abstract: The years whether M_S≥7.0 earthquakes occurred or not are investigated by using the M_S≥5.0 earthquake catalog occurred in the Chinese mainland.The year when an M_S≥7.0 earthquake occurred is called “earthquake year”, and the year when no M_S≥7.0 earthquake occurred is called “no-earthquake year”. The relationships between the annual numbers of M_S≥5.0 earthquakes and “earthquake year” or “no-earthquake year” are analysed, and χ² test method has been employed to test the significance.The results obtained are as follows: ① If the annual nember of the M_S≥5.0 earthqaukes is greater than 30 in some year, the sixth year later is “no-earthquake year”. The test of significance for this relationship can be passed under the significance level of 2 percent; ② If the annual nember of M_S≥5.0 earthqaukes is greater than or equal to 24 in some year, the sixth and ninth years later are “no-earthquake year”. The tests of significance for these two relationships can be passed under the significance level of 10 and 2 percent respectively; ③ If the annual nember of M_S≥5.0 earthqaukes is less than 10 in some year, the sixth year later is “earthquake year”. The test of significance for this relationship can be passed under the significance level of 2 percent.

Key words: Annual nember of M_S≥5.0 earthqaukes, M_S≥7.0 earthquakes, Significance test, Chinese mainland