Abstract: Based on summarizing the researches of predecessors and combining with our new data obtained by 1:50000 geological mapping in the past few years, we discussed several controversial problems relatedto the seismic fault of the 1668 Tancheng earthquake (M=8 1/2) and put formards some new understandings. These problems include the distribution of the 1668 seismic fault. stick - slipping and creepslipping fault segments, fault fracture mechanism, slip behavior of seismic fault and fault segmentation.