Belonging to the technical field of waste treatment, the invention in particular relates to a purification process for coal fired power plant desulphurization sewage. The method comprises the steps of: 1. adjusting the pH value to alkaline; 2. adding a chelating agent and fully stirring the materials till no generation of floc; 3. adding inorganic high molecular polymer magnetic powder, and fully stirring the materials; 4. adding an organic high molecular polymer, and fully stirring the materials; 5. conducting solid-liquid separation until all the flocs settle, and discharging the lower sediment; and 6. adjusting the pH value to neutral. The process provided by the invention adopts simple system and steps to completely and effectively remove the neutral salt, suspended solids, fluorides, sulfides, heavy metal ions and other harmful pollutants from the sewage, and has the characteristics of low cost and simple operation, etc.