The Sonid Zuoqi ductile metamorphic core complexes, which are located on the south- eastern margin of the CAOB, includes a extensional ductile detachment zone which strike EW and dip to S. The footwall of this detachment zone consists of Permian- Triassic intrusions, ductile shear zone (mylonite zone) and brittle detachment fault zone, and the hangwall composes of Palaeozoic and Proterozoic rocks. The major rock types of the Sonid Zuoqi ductile detachment zone are mylonites which are generally characterized by a down- dip stretching lineation which plunges to 15°~39° toward 185°~228°and well- developed mylonitic foliation (S- C foliation) which dips toward 145°~194° at 34°~55°. At the microscopic scale, the quartz is strongly oriented to wire- drawing and has sub- particle recrystallization. The feldspar forms asymmetric rotational cataclastic system and core- mantle structure. Shear- sense indicators such as asymmetric porphyroclasts, S- C fabric and mica- fish, consistently indicate top- to- the- SW shear. The strong deformation mylonite and Halatu plutons within the footwall of detachment zone are taken as the dating objects and yields zircon U- Pb ages of 244.4±1.8 Ma, 244.0±2.4 Ma and 229.4±2.1 Ma; (U- Th)/He age of 212.5±13.1 Ma and 214.1±13.2 Ma for two strong deformation mylonite and the granite with the detachment zone, respectively. Combined with the regional tectonic background and previous research data, it is considered that the initial deformation time of the Sonid Zuoqi detachment zone was after 244 Ma, and the deformation peak time was 224 Ma and continued to 214 Ma. The cooling rates of the ductile detachment zone of the Sonid Zuoqi metamorphic core complex during 244～224 Ma and 224～214 Ma are 18.5 ℃/Ma and 16.3 ℃/Ma, respectively, and the uplift rates are 0.54 km/Ma and 0.48 km/Ma, respectively. The early simple shear- dominated general shear and the late pure shear- dominated general shear jointly restrict the structural denudation process of the Sonid Zuoqi metamorphic core complex. The results of this paper show that there was a rapid crustal uplift event in the early Mesozoic between the northern margin of North China and the Central Asian orogenic belt, which may be the result of the combined action of the collapse after the final closure of the Central Asian orogenic belt and the far- field effect of the Mongolia- Okhotsk tectonic belt.