Much cleaning solution generated during chemical milling for aluminum alloy must be effectively removed before safe discharge because it has high chemical oxygen demand (COD) due to the presence of triethanolamine. The cleaning solution produced during the chemical milling was treated by fenton oxidation process. The effects of initial pH, H2O2 concentration, c(H2O2)/c(Fe2+) and fenton reaction time of the effluent on CODCr removal rate of the cleaning solution were studied by optimizing test methods. The initial pH had most significant influence on the CODCr removal rate. Based on the orthogonal test, single factor experiment was carried out to further optimize reaction conditions, and optimum conditions for removing triethanolamine in chemical milling cleaning solution by virtue of fenton oxidation process were as follows: pH=2.5, H2O2 concentration=325 mmol/L, c(H2O2)/c(Fe2+)=12.5 and reaction time=45 min. Under such circumstance, effluent CODCr might decrease to 40 mg/L and a CODCr removal rate might amount to 99.1%. The triethanolamine in cleaning solution for chemical milling can be effectively degraded by fenton oxidation process.