A reaction-regeneration device for catalytic dehydrogenation or/and catalytic cracking of alkanes comprises a reaction device and a regeneration device. The reaction device comprises a reactor and a disengager, and the disengager is located at an upper part of the reactor. The reactor comprises a tapering section, and diameters of cross sections of the tapering section gradually decrease from bottom to top. Secondary conversion of alkenes caused by back-mixing is reduced, and thus the yield and selectivity to alkenes are increased.