Abstract: This paper proposed one method, which uses the linear rela tion between the middle-low magni tude and cumula tive frequency to obtain the linear relation betw een magni tude and interval frequency. The maximum ear thquake mag nitude M1 can becalcula ted by using the linear rela tion betw een mag nitude and interval frequency. The calculation resul ts show that: by using the linear relation betw een mag ni tude and interval frequency, the estimated max imum earthquake magni tude M1 is closer to the observ ed maximum earthquake mag ni tude in one seismic perio dorepi sode than tha testimated by using the relation betw een magni tude and cumulative frequency. The later one is oftenov erestimated. The evolutional cha racteristics of the rela tion curv e betw een mag ni tude and cumulative frequency, and the estima ted maximum earthquake mag nitude M1 by using the linear relation between mag ni tude and interval f requency can give the new info rmatio n in the medium- lo ng term earthquake trend prediction for one sei smic period or epi sode. The inv estigation show sthat the seismic episode started from 1979 in China is coming to the end, asei smically quiet period is close to the end in the area of the North-Eastern side of Pamirs.

Key words: Earthquake prediction, Maximum earthquake magnitude, Relation between magnitude and cumulative frequency, Seismic period or episode