Abstract: The fuzzy mathematics theory with accordance to the method of site types partition of "Code for seismic design of buildings" (GB 50011-2001)is applied to deduce the fuzzy quadratic appraisement method of site types, fuzzy vector and fuzzy characteristic period of site types is put forward, which achieves continuum of site types partition. Based on the collected datum of site types, the geo-model is constructed, which makes fuzzy isolines of site types and characteristic period available. In comparison with real datum measured, the site types by this fuzzy isoline is consistent with site types defined by "Code for seismic design of buildings", and fuzzy characteristic period are consistent with the period from the code very well, which justifies the significance of fuzzy isoline to seismic construction design.