Abstract: The catalytic oxidation treatment of radioactive trioctylamine-xylene(V/V=1/4) organic waste liquid containing transuranic nuclides(total α activity: 10⁸ Bq) using commercially available nano-MnO₂ as the catalyst was investigated in the present work. The process aims to convert organic components into non-dispersible solid residues while minimizing radionuclide release. The simulated experiments were conducted to validate the process over 90 hours of continuous operation. Results demonstrate that the trioctylamine-xylene mixture is predominantly decomposed into carbon dioxide, water, and trace small-molecule organics, achieving an inorganic conversion rate exceeding 95%. Key reaction parameters, including a reactor temperature of (190±20) ℃, stirring rate of 30 r/min, and feed rate of 87 mL/h, are optimized to ensure stable operation. Post-reaction analysis reveals that residual carbon content in the catalyst increased from 0.044% to 2.08%, indicating minor carbon deposition. Tail gas analysis detects volatile organic compounds(TVOC: 925.1 mg/m³), predominantly xylene(660.60 mg/m³), alongside trace benzene, toluene, and olefins, suggesting partial catalytic oxidation and chemical reforming pathways. Notably, trioctylamine exhibits higher catalytic degradation efficiency compared to xylene, likely due to its stronger polarity. Nitrogen oxides(NO: 0.05 mg/m³, NO₂: 0.52 mg/m³) in the tail gas are minimal, implying nitrogen retention in solid residues or conversion to N₂. Subsequent experiments in hot cell were successfully carried out to treat radioactive waste liquid under optimized conditions. Post-treatment radionuclide balance calculations reveal that ＞98% of transuranic nuclides are retained in catalyst residues and reactor internals. Less than 0.001% of nuclides are released via gaseous pathways, confirming effective containment. Solid residues constitute 96.86% of the original activity. The catalytic oxidation system demonstrated robust performance in converting liquid organic waste into stable solid residues under mild conditions(190 ℃, atmospheric pressure), avoiding secondary pollution risks compared with high-temperature incineration or corrosive supercritical oxidation. This work validates catalytic oxidation as a viable method for treating radioactive organic liquids, particularly for small-batch operations. The process achieves high radionuclide immobilization while enabling safe gas-phase discharge, offering significant advantages over conventional cementation(e.g., volume expansion, leaching issues) and glass vitrification(incompatible with organics). Further optimization of catalyst formulations and tail gas treatment can enhance decomposition efficiency for complex organic matrices.