Abstract: After World War Ⅱ, the Allies put into effect an imposed democratization reform in Germany for permanent erasing German threat to the peace of the world. It consisted of Demilitarization, Deindustrilization, Denazafication and Democratization, known as four Ds. The most important and controversial policy among them was the Allies' Denazification in the western zone of Germany. Denazification was a significant historical event in western German history after World War Ⅱ. It exerted important effects on German political tends. This thesis will focus on the propounding, the practices and the effects of Denazification.