Abstract: A comparative study of visible light photosensitization alone and US/ photosensitization was made to evaluate their respective effectiveness for removal of hard-degraded pollutants from water with 4, 4′- dibrominated biphenyl（4, 4′-DBB）in the experiment, and the degradation degree was estimated by the change of ultraviolet absorption curve. The results indicated that both processes worked well. Especially，a further enhancement of the removal of 4, 4′-DBB was achieved in the process assisted by ultrasound. Six kinds of photo initiators were chosen to treat 4, 4′-DBB solution under visible light. The final removal rate of 2 mg/L 4, 4′-DBB solution reached 22.9% after reacting for 30 min，when Funchsin basic（FB）was chosen as the sensitizer and pH=6. After 28 kHz ultrasound was added，the removal rate of 2 mg/L 4, 4′-DBB solution was enhanced to 25.6%. It was also found that 4, 4′-DBB’s removal by the two methods followed pseudo-first order reaction and the enhancement factor f for 4, 4′-DBB removal rate constant was about 1.12.