Put forward a new method to prepare polyaluminium ferric chloride (PAFC). Discuss the effect of starting materials, reaction processes on the leaching ratios of alumina and iron oxide. Application properties were tested. The results showed that both diasporic bauxite and the red mud from gibbsite (RMG) do not need to be baked. In the case of diasporic bauxite, the leaching ratios of alumina and iron oxide reach 4.15% and 78.32% respectively under the conditions that the concentration of hydrochloric acid is 6mol/L, the reaction time is 60 minutes, the reaction temperature is about 109°C, and the way of extracting is two-step extracting. In the case of RMG, the leaching ratios of alumina and iron oxide reach 89.00% and 98.39% respectively under the same conditions. Diasporic bauxite is not a suitable raw material for PAFC synthesizing. The PAFC prepared from RMG was used to treat active black KN-B dye-containing wastewater and the Kaolin-containing wastewater. The maximum depollution ratio is 98.0% and 97.0 % respectively.