The Qinling—Tongbai—Dabie collision orogenic belt is the largest highultrahigh pressure structural zone in the world．There are two large ductile shear zones on both sides of the orogenic belt，and geological scholars have done more study on the Yindian—Malong shear zone in the south of Tongbai complex. But there is few study on the shear zone in the north of Tongbai complex. This project uses a variety of methods to study and cognize the large ductile shear zone intensively，but also discusses its ascription.Methods：On the basis of detailed field observation，we combine the analysis of indoor microstructure analysis，finite strain measurement，vorticity calculation，dynamic recrystallization of quartz and feldspar，hornblende total Al pressure gauge，hornblende—plagioclase—quartz thermometer and single mineral thermometer of biotite to study the shear zone in northern boundary of Tongbai complex. And according to these features of the shear zone，we make comparative analysis with the Shangdan fault in the west and the Xiaotian—Mozitan shear zone in the east to limit the ascription of the shear zone in northern boundary of Tongbai complex. Results：Through our observation and analysis，we found that the shear zone in northern boundary of Tongbai Complex is a sinistral ductile shear belt，and the shear zone developed rodding structure with layer structure．There is a special detachment surface binding between layers．Through microscopic analysis and measurement we know that the finite strain measurement value Rxz is between 1.80~2.04，and the average is 1.95，the vorticity value Wk is between 0.82~0.90，the average is 0.86，which is greater than 0.75 and indicates that the shear zone in northern boundary of Tongbai Complex is mainly simple sheared，supplemented by pure shearing. Through the dynamic recrystallization of quartz and feldspar and hornblende total Al pressure gauge，hornblende—plagioclase—quartz thermometer and Ti in biotite thermometer，we know that the formation conditions of the shear zone in northern boundary of Tongbai Complex are about t=560~684℃，P= 0.6~0.9 GPa，belonging to the high amphibolite facies，which is in a crustal rheological layer position． Conclusions：Through our detailed field observation and indoor analysis on the shear zone in northern boundary of Tongbai complex，we know that the shear zone is a sinistral ductile shear belt and develops rodding structure with layer structure. The vorticity value indicates that the shear zone in northern boundary of Tongbai Complex is mainly simple sheared，supplemented by pure shearing，reflecting the shear band’s formation is not only influenced by extrusion，but also affected by the force paralleled to the orogenic belt，which may be related to the mechanism of reentry after collision of orogenic belt. By the comparison with the Shangdan fault zone and the Xiaotian—Mozitan shear zone we can know that the shear zone in northern boundary of Tongbai Complex belongs to Xiaotian—Mozitan shear zone，rather than the Shangdan fault zone．