Abstract: A method for evaluating the stability of crude emulsion system was established based on Turbiscan stability analyzer and the influence of chemical viscosity reducers, including three water-soluble one and seven oil-soluble one, on the demulsification of Tahe oilfield produced fluids was studied. Test results indicated that all these three water-soluble viscosity reducers showed negative effect on demulsification, yet oil-soluble one did not show negative effect, in which THY-3 even showed significant positive effect on demulsification. It was found that the influence of water-soluble viscosity reducer on the demulsification of oilfield produced fluid was depended on its viscosity reduction performance, e.g. THS-1 viscosity reducer exhibited the best viscosity reduction performance with a reduction rate of 95.35%, it could improve the stability of crude emulsion significantly, at the same time, its negative effect on demulsification was also significant; the viscosity reduction rate of THS-2 was 82.58% and it showed less negative effect on demulsification of oilfield produced fluid.