Abstract: A defoamer of polyether silicone was prepared for reducing the bad foam in technological process. In the presence of Pt catalyst, methyl end-group hydrogen silicone (PHMS) reacted with propylene-polyether ether to form a polyether silicone (PESO). Chemical structures of PESO and their performance were characterized. The effects of PESO with different structures on the defoaming ability were investigated. Experiment results showed that end-group polyethylene siloxane is characterized by better water-solubility, speedy defoaming, and long-term inhibitation of foam. Though the foam inhibiting ability improves obviously with increasing the molecular weight of PESO, its appearance and storage stability are influenced.