Abstract: The authors have obtained a lot of rock finite strain data from a basement ductile shear zone in the Shaoxing-Jiangshan fracture zone. Analysis shows that this ductile shear zone has the features of inhomogeneous simple shear strain. Its displacement field belongs to Ramsay Ⅰ type and the strain is of flattening type. The ratio of the long axis to short axis, shear strain value and strain intensity decrease from the center of the shear zone outwards and shear direction is sinistral in plan. The longitudinal extension is 102.1 km, the lateral shortening is 5, 76 km, and the horizonatal shear displacement is 42 km.