The invention relates to a viscous oil produced liquid demulsifier and a preparation method thereof. The method comprises the following steps: using toluene as a solvent and p-toluenesulfonic acid asa catalyst, and reacting polyether glycol with maleic anhydride to obtain maleic acid polyether ester; using toluene as a solvent and chloroplatinic acid as a catalyst, and reacting hydrogen-containing silicone oil with acrylic acid, methyl acrylate and the prepared maleic acid polyether ester to obtain a comb-shaped silicon modified polyether compound. The demulsifier has good demulsification anddehydration effects on oil field viscous oil produced liquid.