Abstract: In order to explore the effect of quality of water for pulp conditioning on bubble size distribution in flotation process, a study is made on the characteristics of bubbles size distribution when the water used varies in quality by using image analysis method, so as to make known the effect of variation of concentrations of Ca²⁺ and Al³⁺, and pH value and hardness of water on bubble size distribution. As indicated by test results, with the increase of concentrations of Ca²⁺ and Al³⁺, the average bubble size tends to decrease and stay constant at time when the ion concentration reaches the critical merging concentration of 10⁻² mol/L; with the increase of pH value, the average bubble size fist increase and then decrease and reaches a highest value at a pH value of 7, and when the solution becomes acid （pH < 7）, which is larger than the average bubble size when the solution is alkali with a pH value of > 7; and with the increase water hardness, the average bubble size tends to gradually diminish and stay unchanged when the hardness reaches the critical merger concentration of 600 mg/L CaCO₃, with an average size stabilized at 0.45 mm. The research-derived achievements provide both theoretical and technical support for regulating bubble size in pulp conditioning and improving bubble mineralization effects.