In this paper, the author first studied characteristics of tectonite of ductile shear deformation in the epimetamorphic microclastic rocks, and made classification of tectonite. Then, the difference of this tectonite from typical felsic mylonite was elaborated. Based on petrofabric characteristics and comprehensive analysis, the author holds that the deformation mechanism of tectonite was mainly intergranular movement and partly intragranular deformation, and that it occurred in the superzone of the crust at the depth of 5-8 km under the conditions of lower pressure and lower temperature.