Two kinds of polyorganosiloxane (POS), DVTMS&B (DB) and TMTV&B (TB), were synthesized by copolycondensation of 1,3-divinyltetramethyldisiloxane (DVTMS) or tetravinyltetramethylcyclotetrasiloxane (TMTV) with component B in polydimethylsiloxane (PDMS), respectively. The PDMS/DB(TB)/PAN composite membranes with tri-layer, a polyacrylonitrile (PAN) support layer, a DB(TB) transition layer and a PDMS active layer were prepared by sequential coating methods and used to the separation of 1% (?) aqueous solution of n-butanol by means of pervaporation. The effects of mass ratio of DVTMS or TMTV to B and the mass content of DB and TB in casting solution on pervaporation performance were investigated. The results showed that the addition of DB or TB enhanced pervaporation performance of composite membrane with a same total thickness of separation and transition layer. To 1%(?) aqueous solution of n-butanol, the separation factor was 40.96 and permeation flux was 628.40 g/(m2?h) of PDMS/DB/PAN composite membrane, under the mass ratio of DVTMS:B of 3:1 and the concentration of DB in transition layer solution of 5%(?), and the separation factor was 41.58 and permeation flux was 540.00 g/(m2?h) of the PDMS/TB/PAN, under the mass ratio of TMTV:B of 1:1 and the concentration of TB in transition layer solution of 3%(?). Thus, the separation factors were increased by 8.5% and 10.2%, along with the permeation fluxes were increased by 29.5% and 11.3%, respectively, of PDMS/DB/PAN composite membrane and PDMS/TB/PAN composite membrane compared with the same thickness PDMS/PAN composite membrane under the optimized conditions.