Abstract: Terephthalic acid can be obtained in the presence of a catalyst CdCO3 by isomerization of potassium salt of coal acid (water-soluble acids, WSA) produced from coal oxidation. Effects of the amount of catalyst, initial pressure of CO2, reaction temperature and reaction time were investigated. It was confirmed that WSA can be converted to terephthalic acid in the presence of a catalyst. In case of isomerizing the potassium salt of coal acids alone, the optimum conditions of isomerization were found to be: temperature 430 ℃～450 ℃, initial pressure of CO2 4.0 MPa, catalyst CdCO3 4% and reaction time 2 h. Such optimum conditions were similar to those of the isomerization by a mixture of potassium coal acids (WSA) and potassium benzoic acid (BA). The yield of crude TPA by isomerization of potassium salt of coal acid was about 34%, which was equivalent to 75% of BPCA(theoretical yield), and was the effective composition of WSA. It has shown that the selectivity was good. The yield of crude TPA was about 68% if isomerization was carried out with a mixture of potassium salts of coal acid and benzoic acid at its optimum conditions. The yield of TPA was as high as 70% after being deducted from the theoretical yield of BA dismutation, and about two times of WSA isomerization alone.The purity of the refined TPA was ≥ 99%.