Abstract: In order to realize the harmless treatment and reuse of coalbed methane produced water in Qinshui basin, according to the characteristics of the coalbed methane produced water in Qinshui basin, the produced water was treated by coagulation-Fenton oxidation method. Firstly coagulant was added into produced water, t hen Fenton reagent was added into the produced water after coagulation treatment. The results showed that the removal rate of suspended matter was about 100%, the removal rate of COD was 97. 29% and the removal rate of chroma was 98. 89%, the produced water treated by coagulation-Fenton oxidation method reached the prima ry standard of GB 18918- 2002 Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant. The damage degree of reservoir caused by Qinshui river water and the treated produced water was evaluated by formation sensitivity flowing experiments. The results showed that the damage degree of reservoir caused by Qi nshui river water was 52. 87%, but the damage degree of reservoir caused by the treated produced water was only 4. 86%, the treated produced water as drilling fluid h ad excellent ability of reservoir protection.