The invention relates to a high-power microwave source device in the field of high-power microwave technology, in particular to a coaxial double annular cathode on-line adjusting device applied in RBWO, comprising a cathode rod, an outer cathode head, an inner cathode head, four radial rotary transmission rods, four axial rotary transmission rods, four axial horizontal transmission rods, four connecting pins, four radial adjustment bevel gears, four axial adjustment bevel gears and four servo motors. The whole structure is rotationally symmetrical about the central axis. The invention overcomes the complexity of frequency tuning RBWO regulation mode, By adjusting the extension and retraction of the inner and outer cathodes, the wide frequency spacing across X and Ka bands can be fine-tuned, and the dual-band output can be realized simultaneously. It is of great significance for the design of this type of devices.