Abstract: Effects of some factors were studied on the degradation of 4 chlorophenol in wastewater by pulsed high voltage discharge plasma. Furthermore, the intermediate products of the degradation were identified . The degradation efficiency of 4 chlorophenol could be raised considerably by increasing the peak voltage, prolonging the discharge time and adding FeSO 4 to the wastewater solution. The addition of radical scavenger and buffer could decrease the degradation efficiency of 4 chlorophenol. The maximum degradation efficiency of 100 mg/L 4 chlorophenol was over 90% after discharging for 240 minutes. The main intermediate products were phenol, hydroquinone, catechol, 1,4 benzoquinone and 4 chlorocatechol. The 4 chlorophenol can be mineralized to CO 2 and H 2O by enough time discharge.