A new quaternary ammonium modified amino polysiloxane (QASO-121)was synthesized by the quaternized modification of N,N-two methyl-γ-aminopropyl-γ-aminopropyl poly two methyl siloxane (ASO-121) using ethyl chloroacetate.The chemical structure of QASO-121,its emulsion and membrane configuration on fibers surface were characterized by infrared spectroscopy (IR),nuclear magnetic resonance spectroscopy (1HNMR),scanning electron microscopy (SEM),nanoparticle size analyzer and other instruments.The effects of its ammonia value,viscosity,pH and silicone emulsion dosage on the performance of treatment of cotton fabric were also discussed.The results show that the average particle size of the QASO-121 emulsion was 75.3 nm,potential was 21.2mV, and it had a good film-forming ability on fabric surface.The softness and hydrophilicity of fabric increased,the whiteness of fabrics remained the same,when the ammonia value of QASO-121 was 0.6 mmol/g,the viscosity was 2.600 Pa?s, the amount of the emulsion was 4g/L.Comparing the application performance of QASO-121 and not the quaternization of ASO-121,it is find that they had a similar effect on the softness of finishing fabric,but the finishing fabric using QASO-121 was full of elasticity and possessed the improved hydrophilicity,its yellowing resistence was also improved.