Abstract: In order to study the shutdown and restart characteristics of polymer flooding heavy oil produced fluid, the horizontal loop device was used to conduct the test to simulate the shutdown and restart process of polymer flooding heavy oil produced fluid pipeline, in which the changes of pressure and flow of polymer flooding heavy oil pipeline with time during its shutdown and restart were analyzed, the effects of water content, polymer, oil temperature and other factors on restart pressure were explored, and the yield characteristics of produced fluid were studied. The results show that during the restart process, the pressure and flow in the pipeline are less affected by the polymer. The pressure in the pipeline rapidly reaches the peak value, and gradually decreases to a stable level as the produced fluid begins to flow. The variation rule of flow in the pipeline is similar to that of pressure. The inverted point of polymer-containing produced fluid is 30%, while that of polymer-free produced fluid is 40%. When the water content is less than or equal to 30%, the restart pressure of the polymer-containing produced fluid pipeline will be higher than that of the polymer-free pipeline. When the water content is greater than or equal to 50%, the result will be diametrically opposite. When the temperature ranges from 14 to 40℃, the heavy oil produced fluid will have a yield value, which may decrease with the temperature rise, but when the water content exceeds the inverted point, there will be no obvious yield characteristics. Before inversion, the yield value increases with the increase of water content, and the restart difficulty increases with the rise in water content. After inversion, however, the shear stress decreases with the rise in water content and the restart difficulty decreases with the rise in water content, hardly affected by the polymer. The research results of shutdown and restart characteristics of polymer flooding heavy oil produced fluid can be used as a reference for economic and safe operation of oil field gathering and transportation pipelines.