In this work, the polyamidoxime functionalized magnetic graphene oxide (mGO-PAO) was prepared via the surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization, characterized by TEM, FT-IR, VSM, and TGA techniques, and applied for the extraction of uranium(VI) from aqueous solutions in an ultrasonic field. The effects of pH, contact time, initial uranium(VI) concentration, temperature, and competitive ions on the adsorption of U(VI) were investigated. The adsorption speed of mGO-PAO for U(VI) was found to be 18 times faster in the ultrasonic field than in the shaking mode, and the adsorption equilibrium, to be reached within 2 min. When the U(VI) concentration was 10 mg/L, the temperature, 298 K, and pH, 6.0, the removal rate of U(VI) reached 98.24% with high selectivity. The adsorption kinetics and isotherm data were well described by the pseudo-second-order and Langmuir models, respectively. The thermodynamic parameters suggested that the adsorption of U(VI) was a typical spontaneous and endothermic process. XPS analysis suggested that the mGO-PAO bound the U(VI) through the eta(2)-N,O binding mode. Moreover, the mGO-PAO exhibits excellent adsorption performance in actual radioactive wastewater with an assist of ultrasound. This work provides a new approach for highly effective extraction of U(VI) from the actual radioactive wastewater.