Abstract: The results of mylonite mass balance analysis show that the Eshankou ductile shear zone was formed by nonisochemical metamorphism in an opening system. The gain and loss of components occurred mainly in the tectonic muscovite quartz schist stage, which was characterized by the introduction of large amounts of LOS （fluid）, SiO 2, Fe 2O 3, FeO, TiO 2 and K 2O and obvious removal of Na 2O. Al 2O 3 was kept at a constant. The entire shear zone gained about 50% of mass and volume when the protoliths changed to muscovite quartz schist.