<p>This paper proposes a vortex boundary identification method for compressible flows based on the interaction between Liutex and shear. The Liutex-Shear (RS) interaction equation, originally developed for incompressible flows, is extended here to account for compressibility effects. A number of test cases ranging from subsonic to transonic flows using discontinuous Galerkin method are conducted to investigate the proposed method. Different terms in the proposed RS interaction equation are computed for the Taylor-Green vortex and flow past a cylinder with different Mach numbers to investigate the mechanism. It is demonstrated that the vortex boundary can be accurately identified through the viscous term, which exhibits pronounced dissipation characteristics. This approach is grounded in robust theoretical and physical principles and eliminates the need for arbitrary threshold selections. Future work may extend this method to 3-D flows across all speeds, offering a physically consistent approach for vortex boundary extraction.</p>