With polyoxyethylene polyoxypropylene epoxy ether and polyoxyethylene polyoxypropylene ether as the branched chains,polysiloxane as the based chain,under the isopropyl alcohol solvent,using chloroplatinic acid as the catalyst,through silicon hydrogen addition reaction, synthesized the polyether polysiloxane crude oil demulsifier.Fixed n (epoxy ether) : n (methyl ether) = 1:1, the research shows that n (Si—H) : n (C=C) = 1:1.15, temperature 105 ℃, the reaction time of 5 h, 30 ug/g catalyst and solvent dosage 40% overall (raw material), the conversion rate reached 92.62%, and by FTIR and 1H NMR had been used to characterize the structure of the product, spectra analysis shows that expected product was synthesized. Its critical Angle beam is determined by the surface tensiometer 0.7 g/L, minimum surface tension of 24.2 mN/m. The Demulsifier in demulsification temperature 70 ℃, the amount of 100mg/L, to Yanchang Yongping crude oil dehydration rate reached 88.42%, has good demulsification performance.