By using the Leibo area as an example, a basic understanding of the latest deformation style in the Mabian seismictectonic belt has been abtained, based on the geologic and geomorphologic survey, and combined with trench technology and dating. The research results demonstrate the existence of an NEEtrending Leibo fault zone in the Leibo area. A faulted stratrum age is about 40 ka. The fault is a dextrak slip and active in latepleistocene. The NNWtrending Manao fault exposes the Quaternary weathering crust, from which two displacement events can be recognized. Their displacement offsets are 0.5m and >0.7m in sections respectively. A steep plane of the offset provides the evidence of horizontal sinistral slip. The NEE and NNW trending faults in the Mabian seismic zone belong to one pair of conjugate shear faults in the modern tectonic stressfield, representing the latest deformation style of the Mabian seismotectonic zone. The disastrous earthquakes in the Mabian seismotectonic zone are characterized by moderate magnitudes, high frequency and weak zoning, and these are in agreement with features of earthquakes caused by conjugate tectonic frame. The Mabian seismotectonic zone is situated at the southern section of the eastern margin of the Tibetan Plateau. The research further shows that a ductile flow model in the middlelower crust, controlled by gravity, can give a reasonable explanation about the active habits of faults, including the Dalianshan fault zone, Anninghe fault zone and Xianshuihe fault zone. With a continuous flow of the middlelower crustal material inside the Tibetan Plateau, the Plateau boundary spread gradually outwards and a new boundary formed. Thus the boundary represents a newlyformed seismotectonic belt.