Abstract: Technical upgrading work is made on the pulp preprocessing unit of the plant’s flotation system through the use of gravity-flow preprocessor for further improvement of flotation performance and reduction of consumption of agents.The paper presents an introduction to the structure,working principle,technical features of the gravity-flow pulp preprocessor,and the effect of its field application at the plant.Practice shows that the application of the pulp preprocessor has achieved the remarkable effect as follows: in addition to an increase of the capacity of the flotation system by 12.18% and a rise of the flotation perfection index by 3.18 percentage points,the consumptions of collector and frother are reduced respectively by 31.78% and 11.41%,and the qualification rate of ash of concentrate is increased from 70% to 90%.