This study investigates the characteristics of acetic acid decomposition on a negative DC corona discharge over water. The corona discharge is 4 mm away from the water surface. Furthermore, this study explores the mechanisms involved in the chemical reactions of active species during water treatment, using discharged plasma. During processing, oxygen or ozone is supplied to the reactor. The results of experiment and simulation show the same trend on time variation of acetic acid concentration. Therefore, the simulation model that considers the supply of ozone, hydrogen peroxide, and can confirm the change in acetic acid concentration. Our results indicate that negative ions such as can be used for water treatment by DC corona discharge.