The invention discloses a treatment system for purifying produced water and a treatment method thereof, and belongs to the field of oil and gas exploitation. The treatment system for purifying produced water comprises a membrane separation device, a fine suspended solid separation device, a first pipeline, a second pipeline, a first pipeline mixer, a second pipeline mixer, a third pipeline, and afourth pipeline; a ceramic adsorption layer, a quartz sand filter layer, and an activated carbon adsorption layer are arranged from bottom to top in sequence in the fine suspended solid separation device; the first pipeline and the second pipeline are both used for conveying purified produced water, the first pipeline communicates with the inlet at the bottom of the fine suspended solid separationdevice, the two ends of the second pipeline communicate with the outlet at the top of the fine suspended solid separation device and the inlet at the top of the membrane separation device respectively; and the first pipeline mixer and the second pipeline mixer are sequentially arranged on the first pipeline in the direction of water flow; the third pipeline communicates with the side wall of thefirst pipeline mixer for delivering a first medicament; the fourth pipeline communicates with the sidewall of the second pipeline mixer for delivering a second medicament.