Thermal activation of persulfate (PS) is an effective method for degradation of organic pollutants, but the high temperature has become restrictive factor. The effects of active carbon (AC) on the thermal activation of persulfate (PS) and the subsequent degradation of p-nitrophenol (PNP) in water was systematically investigated. The effects of critical parameters, including the initial pH, PS concentration and dose of AC were also investigated. AC could significant enhanced thermal activation of PS for high efficient degradation of PNP. The degradation efficiency of PNP reached 100.00% in AC/PS system, whereas only 31.69% in PS system with AC, PS, and PNP concentration of 1.0g/L, 2.0mmol/L, and 10.0mg/L, respectively, initial pH of 3.5, temperature of 50℃ and reaction time of 120min. Free radical quenching experiments demonstrated that the AC/PS/PNP system was radical reaction, and SO₄·^- and ·OH were involved in the AC/PS/PNP system, and the SO₄·^- were the main radical for the PNP degradation. The mechanism analysis revealed that the defective sites on AC were involved for weakening the O-O bond in PS and subsequently cleaving O-O bond by heat to generate sulfate radical. The analysis of degradation intermediates suggested that AC could only accelerate the degradation efficiency of PNP but not alter the reaction pathway in PS systems.