Abstract: In order to solve the problems of amino modified silicone such as emulsion floating oil, yellowing easily and hydrophobic of the finished fabric. A kind of block type polyether amine modified polysiloxane was synthesized with polysiloxane terminated with epoxy and polyether terminated with aminopropyl(ED-600) as raw materials, by nucleophilic ring-opening reaction of epoxy group with amino. The Influence of relative molecular weight of polysiloxane segment of polydimethylsiloxane terminated with epoxy on the epoxy groups conversion rate, the properties of emulsion, and the properties of finished fabric were studied, the relative molecular weight of polysiloxane segment was optimized, the properties of modified polysiloxane emulsion and its finished cotton fabric were measured. The results indicated that: as the relative molecular weight of polysiloxane was 4300, the epoxy groups conversion rate was high; the Mn of modified polysiloxane was 1.73×104, the molecular weight distribution of modified polysiloxane was narrow; the modified polysiloxane emulsion had stable property and no floating oil, the average particle size was 54 nm; compared with the fabric finished by amino silicone and side-chained polyether modified amino-silicone, the fabric finished by the modified polysiloxane had better softness, hydrophilic and lower yellowing.