Abstract: Shear banding in polymer fluids represents a paradigmatic example of strain localization under strong nonlinear shear flow, with its physical origin and regulatory mechanisms standing as central scientific questions in polymer rheology. This review synthesizes recent advances in understanding shear banding, focusing on its intrinsic nature, formation mechanisms, dynamic evolution, and stability. Large-scale molecular dynamics simulations have firmly established shear banding as an intrinsic bulk phenomenon under specific shear conditions, often accompanied by a stress plateau in the steady-state shear stress?shear rate curve. Emerging studies reveal that the spatial localization of shear bands is determined by the initial structural heterogeneity of the entanglement network, where pre-existing "weak spots" in the equilibrium state, such as regions with sparse multiple entanglements, act as nucleation sites for shear stain concentration. Investigations on bidisperse systems further demonstrate that chain-length-dependent migration and selective enrichment drive a "fast-band softening?slow-band hardening" coupling mechanism, which is critical for the long-term stability of shear bands. This paper summarizes the key controversies, challenges, and future research directions in shear band studies. It emphasizes that achieving effective prediction and regulation of shear bands, through the development of high spatiotemporal resolution in-situ characterization techniques and the advancement of multi-scale simulations and theories, will provide critical theoretical support for guiding the precision forming of polymeric materials. This includes controlling rheological uniformity in processes such as injection molding and extrusion, as well as enabling the controlled fabrication of advanced products like ultra-thin films and ultra-fine fibers, thereby significantly enhancing processing efficiency and product performance.

Key words: Shear banding, Nonlinear rheology, Entanglement, Strain localization, Molecular dynamics