FIELD: chemical industry. SUBSTANCE: claimed method for preparing terephthalic acid comprises catalytically oxidizing para-xylene in liquid phase to obtain raw terephthalic acid containing 4-carboxy benzaldehyde as the main impurity, and treating raw terephthalic acid with hydrogen in the presence of hydrogenation catalyst in reaction vessel to obtain purified terephthalic acid containing 4-carboxy benzaldehyde in fixed amount which makes it possible to achieve stationary state after partially deactivated catalyst is replaced by new catalyst. The claimed method comprises feeding into reactor raw terephthalic acid which contains 4-carboxy benzaldehyde in amount that exceeds amount in stationary state, and treating terephthalic acid till said treatment attains stationary state. EFFECT: more efficient preparation method. 6 cl, 1 tbl
