This paper deals with earthquake sequence of magnitude over 7.0 in Tianshan region after 1900. It is shown by the M-T diagram that the earthquake activity of magnitude over 7.0 in Tianshan region is just the third activity period at present. The existence of linear trend is negated by the test. The testing result of the period of significance shows there are two periods which are 3 and 5 respectively when the test level is α=0.2. It has been done in this paper to have extrapolated prediction by these two periods, to verify the stability to the remained sequence and to have extrapolated prediction by higher autoregression model.