Highly efficient removal of U(VI) from mine radioactive wastewater has received a lot of attention. Herein, the polyamidoxime/polyethyleneimine magnetic graphene oxide (mGO-PP) adsorbent was successfully prepared by in situ polymerization of acrylonitrile on magnetic GO (mGO) covalently modified with polyethylenimine (PEI). The mGO-PP was characterized by Fourier transform infrared (FT-IR), scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometer, and X-ray photoelectron spectroscopy (XPS). The maximum adsorption capacity of mGO-PP toward U(VI) was 606.06 mg/g at 298 K and pH 6.0. The removal of U(VI) by mGO-PP for U(VI) was a monolayer chemisorption based on the study of the batch experiment. The calculated thermodynamic parameters indicated that the removal of U(VI) by mGO-PP was a spontaneous and endothermic process. The adsorption mechanism of mGO-PP toward U(VI) was explored by FT-IR and XPS analyses. Furthermore, the removal rate of U(VI) by mGO-PP is 93.68% and the K-d value for U(VI) is 444.73 L/g in actual mine radioactive wastewater, and the residual U(VI) concentration (6.37 mu g/L) in wastewater was lower than the maximum permissible concentration of uranium in drinking water (30 mu g/L) (World Health Organization). This indicated that the mGO-PP composite is a promising adsorbent for efficient removal of U(VI) from practical mine radioactive wastewater.