Based upon the analysis of regional geotectonic background of the Tianshui area, in this paper it is emphatically pointed out that Lojiapo earthquake of magnitude 7(1)/(2) in 1654 occurred at the most deep depression of Tian-Li basin since Kainozoic Era, where the conjunction portion was formed as a result of the interaction of the structure in NE trend with active structure in NNW trend. The tectonic conditions of the occurrence of Tianshuizhen earthquake (Ms=6) in 1936 and the causes of the formation of Tian-Li basin are also discussed.