Provided are a method and device for producing negative oxygen ions, and a method and device for purifying air. Said method for producing negative oxygen ions comprises: respectively introducing air and water into an air-water reactor so that the introduced air and water reach a relative movement speed of not less than 20 m/s in said air-water reactor and react within said air-water reactor so as to produce negative oxygen ions； and separating the air containing the negative oxygen ions after the reaction from the water after the reaction, and releasing the air containing the negative oxygen ions after the reaction into a required space. Said method and device can produce a large number of negative oxygen ions and purified air with a high efficiency at a low cost, without producing any harmful substances such as ozone and oxynitrides, and are long-acting and free of maintenance.
