Abstract: Bohai SZ36-1 Oilfield is currently the only one that has industrial application of association polymer flooding. There are complex conditions existing there such as limited space of offshore platform, sand control completion with wire wrapped screen and gravel pack, and high volume production in single layer. Viscosity loss in the injection allocation process was studied by laboratory and field tests. Results showed that mechanical shearing of operating system and solution water quality were important factors influencing viscosity loss. Polymer injection sections like injection pump and perforation hole can affect viscosity loss more than 60%. Also, it was found that with bivalent cation content increasing in solution water, the viscosity loss rate of association polymer stepped up. Additionally, fast dissolution way by micelle grinding can result in slight viscosity loss of associated polymer solution. The study provides a reference to improving the effective polymer viscosity and guaranteeing quality of polymer flooding.