Chlorinated compounds are widely used in the chemicals manufacturing industry. They have high toxicity and good stability, leading to the persistent pollution and damage of the ecological environment. In this study, p-chlorophenol (p-CP) was selected as the model, and a new dechlorination system was developed, that is, tannic acid (TA) and sodium hydroxide (NaOH) were used together to activate persulfate (PS). The effect of TA, NaOH, PS, and temperature on the degradation of chlorophenol was investigated. When 200 mg/L of TA, 0.4 M of NaOH and 100 mM of persulfate were used, the degradation efficiency of p-chlorophenol (50 mg/L) can reach 99 wt.%. There is no significant change in degradation efficiency when the reaction temperature is changed from 20 oC to 40 oC. The mechanism on the co-activation of persulfate with tannic acid and NaOH was proposed. The hydroxyl radicals and superoxide radicals play an important role in the degradation of p-CP. The dechlorination system showed excellent degradation performance for the chlorinated compounds, making it to be a potential oxidant for treatment of the contaminated groundwater.