Luoluan fault belt is the boundary between the southern margin of the North China plate and the northern margin of the Qinling Mountains. The deformation details can restore the plate margin deformation during the plate collision process. The trend of Luoluan fault belt is 290°, inclined to NNE inclination for 67°~80°.It is composed of a plurality of subparallel ductile shear belts. The single shear band width varies from a few meters to hundreds of meters, narrow in west, and wide in the east relatively. There are four events the in the Luoluan fault belt, with the second strong plastic deformation forming a largescale of mylonite. Mylonitic lineation plunging, mineral sigma, delta porphyroclasts and quartz vein morphology kinematics indicate that the fault zone was formed by the kinematic characteristics of the south northward subduction combined with sinistral strikeslip. Mylonite deformation characteristics show the deformation mechanism of the Luoluan fault belt is plasticity in the eastern part, and low temperature diffusion creep in the west, grain boundary sliding and crystal plastic deformation mechanism. Plastic deformation sequence in mylonite minerals: calcite Wingdings`C@ biotite Wingdings`C@ quartz Wingdings`C@ plagioclase Wingdings`C@ potash feldspar. The felsic mylonite deformation phase of Luoluan fault belt is from east to west followed by two feldspar deformation of quartz phase, plagioclase deformation phase and quartz deformation phase. Mylonite formation temperature was 300~550℃, and the temperature in the east was higher than in the western. Amphibole aluminum pressure gauge obtained pressure: 0.75~0.95 GPa and phengite pressure is 0.27~0.87 GPa. The differential stress is 0.32~0.41GPa, and the strain rate is 3.92917×10 -11~3.17713×10-16.Cigar shaped strain ellipsoid and more than 0.75 of the vorticity show strong shearing deformation. These characteristics show the Luoluan fault belt is a ductile deformation belt developed in deep leveland the deformation condition is medium temperature and pressure but eastern temperature is higher than that of the west. Differential stress is bigger in the west than in the east. The deformation environment of eastern part is equivalent to the middle crust, while the western part to the upper and middle crust,which indicate that the uplift is higher in the east than in the west. The mylonite deformation of Luoluan fault belt responsed to the second phase of tectonic activity, which truly reflects the Luoluan fault belt with the tectonic structure of physical processes and formation environment. It is of great significance to interpret the forming environment of the Luoluan fault belt.