Under the catalysis of chloroplatinic acid，a polysiloxane heavy oil demulsifier，was synthesized taking methyl terminated polyether，the self-made low hydrogen silicone oil and acrylic nonylphenol polyoxyethylene polyoxypropylene ester as raw materials.The chemical structure were characterized by IR spectroscopy and nuclear magnetic resonance (1HNMR) spectrum．On basis of the single factor test the effects of different factors on the conversion rate of reation，to determine the optimum technological conditions as follows：the reaction temperature was 95 ℃，the reaction time was 7 h，the molar ratio of silicon-hydrogen bonds was 1.0:1.2，the amount of catalyst was 40 μg/g．Under this condition，the conversion rate of reation reached 92.86%.The performance tests show that the synthesized crude oil demulsifier with the optimal conditions exerted better effects．