The work focuses on evaluating wet air oxidation and catalytic wet air oxidation technique to degrade refinery spent caustics (original COD is 250,781 mg/L) in a milder operation conditions (150-200˚C, 0.2-2.5MPa). The results show that: in non-catalyst WAO, the highest COD degradation conversion could reach about 75% when 200˚C, 2MPa oxygen and 300rpm were used. At every temperature, the reaction procedures follow pseudo-first order equations and the activation energy is 45.5 kJ/mol. The reactivity of three main contaminants in wastewater is on the order of sulphide > petroleum > volatile phenol. The COD degradation conversion could improve to about 95% when composite catalyst MnOx-CeOx/γ-Al2O3 (WMn/Wγ-Al2O3=0.5 and WCe/W MnOx/γ-Al2O3=0.4) was used. The pseudo-first order equations also could be applied for catalyst system and its activation energy decreases to 27.2 kJ/mol. The catalyst could improve the degradation efficiency of petroleum and volatile phenol. Their conversions could increase to 85% and 74% respectively after catalyst used.