Abstract: The conventional complexing agents in the electroplating wastewater include oxalic acid, ethylenediaminetetraacetic acid (EDTA), tartaric acid and citric acid. The precise determination of these complexing agents helps to select proper treatment method for electroplating wastewater. The HPLC method is advantaged by its qualitative analysis and quantitative analysis of the complexing agents in real wastewater due to its robust separation capability. However, the metal complexation probably causes the peak tailing, the new stray peaks and the change of the peak shape as well as the peak area, thus reduces the accuracy and the reliability of qualitative and quantitative analysis of the complexing agent by HPLC. The influence of metal complexation on the qualitative and quantitative analysis of the complexing agent was investigated by HPLC. Hydroxide precipitation was used as a pretreatment method to eliminate metal complexation and improve the analytical accuracy of the complexing agent. Nickel-oxalic acid was chosen as a model compound and the influence of metal complexation on HPLC analysis of oxalic acid was studied. TUV-visible spectrometry was applied to verify the impact of metal complexation on the HPLC analysis of oxalic acid. The experimental results showed that nickel ions had little impact on the qualitative analysis of oxalic acid, but had significant influence on the quantitative analysis of oxalic acid. All peaks were symmetrical and peak trailing was not observed. After adding 200 mg/L nickel ions, the retention time of oxalic acid varied only 1.0% while the variation of peak area reached 33.7%. In Summary, hydroxide precipitation eliminated the metal complexation effectively and enhanced the accuracy on HPLC analysis of oxalic acid. The variation of peak area was reduced to 1.7% as pH was adjusted to 9.0.