The invention discloses a Y type cavity all-optical fiber hopping frequency millimeter wave generating device and relates to the technical field of optical fiber communication and millimeter wave optical generation. Both ends of a broadband grating (2) are respectively connected with a pump source (1) and an active optical fiber (3); the other port of the active optical fiber (3) is connected with the input end of a 1*2 coupler (4); both output ports of the 1*2 coupler (4) are respectively connected with the optical input ports of a narrow-band optical fiber grating (6) and a 1*N photoswitch (5); N passage ports of the 1*N photoswitch (5) are respectively connected with the first or second to the N narrow-band optical fiber grating (71)(72) to (7N); the output ends of the narrow-band optical fiber grating (6) and the first to N narrow-band optical fiber gratings are coupled into a path by a (N+1)*1coupler (8); and the output port of the (N+1)*1coupler (8) is connected with a photoelectric detector (9). The laser emitted by two linear resonant cavities forming a Y-shaped cavity generates difference frequency at the photoelectric detector by selecting the stat of the photoswitch, and the hopping frequency millimeter wave is generated.