Based on faults surveying and research data in Tianjin area, through studying tectonic structure, Quaternary activity, deep structure, stress and strain fields and seism on the Tianjin Fault, the activity and tectonic features of the fault are determined synthetically. Using seismo-geological data, and the historical and modern seismic data, the frequency-magnitude relationship model reckoning by 500 years is established and the relationship between the upper limit of maximum magnitude Mmu and at/b is fit. Then Poisson probability model is adopted and quantitative parameters of the south Tianjin Fault in the coming 50~200 years are calculated.