Abstract: The contents of trace impurity 4-Carboxybenzaldehyde(4-CBA)、p-Toluic acid(p-TOL) and Benzoic acid(C₇H₆O₂) intere phthalic acid by high performance liquid chromatography(HPLC) were determined. A Shim-Pack WAX-1 column was used with the mobile phase of 0.1 mol/L NH₃H₂PO₄+6%CH₃OH(pH 4.5) and the detection wavelength was 254 nm. The trace impurity calibration curves had good linearity in range of 0.59～235.20 mg/kg、4.52～392.00 mg/kg and 0.28～24.55 mg/kg and the correlation coefficients were 0.999 8、0.999 7 and 0.999 9 for 4-CBA、p-TOL and C₇H₆O₂ respectively, the average recovery b enzoic acid added was 99.03% (n=6) and RSD was 0.37%.