The reducer plays very important role in the oxide puller.Harmonious gear reducer is a novel reducer,characterized by high transmission accuracy,large loading capacity,simple structure,and big rate ratio.The type of XJ-99 harmonious gear reducer is developed to meet high precise requirement of oxide puller.In the paper,the operating principle and design of the harmonious gear reducer is interpreted in details.The result shows the harmonious gear reducer has the rotation precision of 0.01 mm and the end surface jumpiness of 0.02 mm,which is better than the same one.