In response to the critical national demand for upgrading automotive gasoline quality, the concept of dual reaction zones was developed to intensify both olefin generation and conversion. The successful large-scale implementation of this process has yielded substantial economic benefits and spurred the invention and systematic study of the diameter-transformed fluidized bed (DTFB) reactor, leading to a suite of new catalytic processes. This study begins with the conceptual origins of the DTFB reactor. By analyzing unimolecular and bimolecular mechanisms in hydrocarbon catalysis, the key conditions necessary for maximizing target products are identified. Furthermore, it elucidates the scientific and technological challenges in applying diameter variation to partition the reaction section, highlighting that the primary challenge lies in achieving precise coupling between flow and reaction multimodalities, which necessitates a generalized drag model for accurate prediction of flow regime transitions. Since flow structure is influenced by both macroscopic parameters and local dynamics, a two-way coupled energy minimization multi-scale (EMMS) drag model and a corresponding multi-scale computational fluid dynamics (CFD) approach have been proposed, laying a theoretical foundation for quantitative design of diameter-transformed sections. The subsequent development of ancillary technologies has provided the necessary engineering safeguards for flexible control of temperature, density, and gas–solid contact time in each zone, ultimately enabling the industrialization, large-scale operation, and long-term stability of DTFB-based catalytic technology. Finally, the study outlines several typical processes and their application performance, and prospects future work.