Chimeric antigen receptor T (CAR-T) cell therapy has achieved remarkable success in haematological malignancies, ushering in the era of adoptive cell therapy. In recent years, CAR-T cell therapy has been progressively explored in autoimmune diseases (AIDs), with the goal of inducing deep immune remodelling and durable drug-free remission in selected patients. This review evaluates CAR-T cell therapy in AIDs through three clinically relevant dimensions: depth, breadth, and length. We use this framework to discuss therapeutic efficacy, immune remodelling mechanisms, disease spectra, target selection, long-term persistence and safety, with the aim of supporting more precise and controllable clinical development.