Based on detailed field investigation, this paper systematically analyzed the extensional tectonics in the Yiwulüshan area, western Liaoning Province, and found that the Yiwulüshan metamorphic core complex had developed before Waziyu ductile shear zone formed. Analysis of the mesostructures, microstructures and quartz C-axis fabrics indicates that lower plate, detachment shear zone and the bottom of the upper plate has uniform top-to-the-SSW shear sense. LA-ICP-MS zircon U-Pb dating results of the syn-kinematic leucogranitic dikes from the detachment shear zone and its lower plate show that the Yiwulüshan metamorphic core complex formed between 157 Ma and 147 Ma.