This paper deals with the mechanism of applying tourmaline to purifying Cu 2+_doped waste water based on the study of absorbing Cu2+ ion by tourmaline in water. Factors affecting the absorption of Cu2+ ion in solution, such as diameters, quantity of tourmaline particles, and experimental conditions (pH value, temperature, stirring situation) are studied. The purifying mechanism of tourmaline lies in the existence of electrostatic field around tourmaline particles, which attracts Cu2+ ion and causes Cu2+ to combine with OH-, the dissociation product of hydroxyl at the surface of tourmaline, thus forming precipitation on tourmaline and attaining the aim of purification.