The mylonites occurred in the fracture zones are studied by dynamically recrystallized quartz grains． The natural microstructures in mylonites are simulated and the deformation conditions of mylonitization are estimated by fractal analysis，recrystallized grain size paleopiezometer and flow laws of quartzite． Depending on fractal analysis，the deformation temperature of mylonitization is approximately 600℃，which presents high greenschist facies to low amphibolite facies． The mylonitization occurred at differential stresses of 9． 1 --10. 7 MPa ( lower limits) ． Compared with extrapolation of quartzite flow laws and estimates of fractal analysis，the strain rate of mylonitization is under 10 － 13. 8 /s．