The comb polysiloxane crude oil demulsifier that the main chain was silicone oil and had multi-branched chain was synthesized by the hydrosilylation reaction with the allyl polyether acrylate, methyl acrylate, methyl methacrylate，using isopropanol as the solventand, chloroplatinic acid as the catalyst and at the reaction temperature of 95℃. The author determined the optimum ratio of 3:2:2 by investigating the effects on the dehydration efficiency of the Yan'an crude under different ratios of the allyl polyether ester, methacrylic acid, methyl methacrylate and study the function of comb crude oil demulsifier on the Yan'an crude oil through the the demulsification performance test. In addition, blending the product with TA-1031 in proportion 3:2 at the total plus the amount of 100mg?L-1, at the dehydration temperature of 60℃, made the dehydration rate achieve 91.02%.