The invention relates to a flexible rotor of an ultra-high-speed liquid hydrogen turbo pump, comprising a screw (1), an inducer (2), a compression nut (3), a shaft (4), a first-stage centrifugal wheel (5), and a metal rubber damper device (6), squirrel cage elastic support (7), bearing pair (8), interstage shaft sleeve (9), secondary centrifugal wheel (10), balance piston (11), metal rubber damper baffle (12 ), the first shaft sleeve (13), the turbine disk (14), the large nut (15), the preloaded disc spring (16), the second shaft sleeve (17); the shafting of the flexible rotor of the present invention is bidirectionally extended, Optimize the connection and torsion transmission structure, reduce the mass of the rotor, shorten the cantilever and support span on both sides, work supercritically, the rated speed reaches 80000rpm, the critical speed margin is more than 20%, and has 60%‑100% variable working conditions and axial Force-adaptive balance ability.