The polysiloxane containing unsaturated double bond has been synthesized by using silane coupling agent (KH570) which was hydrolyzed under pH=4 and terminal-hydroxyl polydimethylsiloxane which was prepared by octamethylcyclotetrasiloxane. And then, polyacrylate emulsion that modified by long chain branched polysiloxane containing unsaturated double bond was composed between (Meth) Acrylate and unsaturated long chain branched polysiloxane by free radical polymerization reaction. By this way, the amount of silicone in the copolymer can be achieved by 80%. The obtained polysiloxane containing unsaturated double bond and modified copolymer were characterized by means of FTIR, 29SiNMR. And also the properties of the emulsion and emulsion film were tested. The results shows that KH570 was fully hydrolyzed and then dehydrated with terminal-hydroxyl polydimethylsiloxane, which eventually made unsaturated long chain branched polysiloxane. It also shows that when mass fraction of silicone was 80%, water absorption eventually was 5.3%, and surface free energy was 6.56 mN/m, and the temperature of maximum thermal weight loss rate was 577℃. Hydrophobic property and thermal stability was improved greatly. So, the unsaturated long chain branched polysiloxane modified copolymer emulsion could be used as high hydrophobic and high heat resistant functional polymeric material.