Phenoxy acetic acid was prepared by catalytic oxidation reaction, using phenoxyethanol and oxygen as raw materials. HPLC(liquid chromatograph) was used for quantitative analysis, and FT-IR(Infrared absorption spectrum), NMR (nuclear magnetic resonance) and GC-MS(gas chromatography mass spectrometry) were used for qualitative analysis. Effects of Catalysts, solvents, and reaction conditions on reaction results were investigated. The results show that: N-hydroxy phthalimide(NHPI) is an efficient catalyst, and dimethylglyoxime and cobaltous acetate were suitable cocatalysts, and acetonitrile is a suitable solvent. Phenoxyethanol: 0.1mol, the amount of NHPI is 8% of molar weight of phenoxyethanol, the suitable molar ratio of NHPI: dimethylglyoxime : cobaltous acetate =8: 7.5: 1. Under the suitable reaction conditions: 80 ℃, 0.8 MPa O2 for 6h, the yield of phenoxy acetic acid was reached 68.6%. The plausible reaction pathway was proposed based on GC-MS analysis.