Abstract: As a method of the information forecasting, commensurability information system was mainly applied to studying system characteristics. The difficulty of commensurability information system is the pick-up of commensurable data. This paper adopted the commensurability as module for data partition, and extracted data by the different frequency. According to the commensurability and time order, the M ≥ 8 earthquakes in Chinese Mainland and M ≥ 7 earthquakes in California. The two methods reached the same goal by different routes. The results show that the series of M ≥ 8 earthquakes in Chinese Mainland and M ≥ 7 earthquakes in California are in a sense rather than fully stochastic.