Abstract: Evolution of sequences of maximum earthquake magni tudes since this century in Yunnan region has been systematically analyzed in this paper. The basic variation patterns in each stage of strong-weak cycles for seismic activity have been also revealed, mechanism of which is primarily explored. It is pointed out that periodicity and strong weak alternation of seismic activities are one of the basic features in Yunnan region. Base on this, a sttistical prediction mode of similarity of multidimensional phase space for maximum earthquake magnitude in Yunnan region has been established by chaos theory. The best parameters forming a best prediction mode a realso determined. Finally, the mode is used to check up the accuracy of quantitative forecast and qualitative prediction by extrapolation to maximum earthquake magnitudes for each year in 1987~1997. The result show that when L=1 and 4 years, the average absolute erro rs $\Delta \bar{M}$ are 0.53 and 0.46 respectively. The disting uishing rate for occurrence of M≥6 strong earthquakes is ƒ=0.90, which is hig her than that of natural one of 0.50. This prediction mode is stable, which can be taken as important evidence to judge seismic tendency in Yunna n region.

Key words: Annual maximum earthquake magnitude, Chaos system, Prediction mode, Multi-dimentional phase space