| Taking Tianjin city as research area, the regional crustal stability in Tianjin city is discussed in this paper by the method of fuzzy mathematics, based on the studies of the tectonic stability, the stability of rock, soil medium and surface stability. According to the data of the current crustal deformation, the present tectonic stress field, the measurement of fault displacement and the dating of fault activity, the tectonic stability research integrated analyze and discuss on the present structural activity and seismic activity regularity. Based on the integrated engineering geology exploration, the foundation stability analyze the compressibility and strength of foundation soil. Based on the field investigation, the surface stability integrated analysis the external force geological phenomena and development degree which include the surface subsidence, sand liquefaction, engineering properties, soft soil thickness distribution. As a result, the evaluation of stability can be semi-quantitative research. According to the stability evaluation, four relative stable should be divided in this region, i.e. stable, sub-stable, less stable and instable.Considering the evaluation data of crustal stability of this area, the less stable areas include the areas of Hangu-Ninghe-Panzhuang, Hexiwu town in Wuqing-west region of Baodi. The sub-stable areas include the areas of north higelands and mountainous region of Jixian, plain region in the north of Baodi faults, plain region of Wuqing -Tianjin-Jinghai, plain region in the coastal of Dagang. This division of the regional crustal stability is the same with the conclusion that worked by China Seismic Bureau on the basis of the probability method of earthquake fatalness analysis.
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