Abstract: Common heavy oil reservoir in Block B125 of the Gucheng Oilfield shows strong heterogeneity, and the average crude oil viscosity is above 1 000 mPa·s, which makes it more difficult to further improve oil recovery rate. Technical advantages of ultra-high molecular weight polymer in enhancing the recovery factor of common heavy oil were evaluated through viscosity, rheology and oil displacement tests. The effect of sulfur-containing sewage on the performance of polymer solution was investigated. The tests show that ultra-high molecular weight polymer has a superior viscosity increasing property, and the viscosity is more than 40% higher than that of conventional polymers at the same mass concentration, and its recovery factor is 3.4 percentage points higher than that of the conventional polymers with the same viscosity. Sulphur-containing sewage will reduce the viscosity of polymer solution over 10%, the recovery factor can be decreased by 3.0 percentage points, and elasticity will be significantly weakened. A total of 22 polymer injection wells were deployed in Block B125. By the end of 2018, a total of 0.22 PV of polymer solution was injected, and the injection pressure increased 3.5 MPa. The daily oil production rate increment was 45.0 tons and the cumulative oil production increment reached 1.84×10⁴ t, while water cut was decreased by 9.0 percentage points and EOR was increased by 1.19 percentage points in this stage. The research demonstrates that the ultra-high molecular weight polymer flooding technology can bring a largely increased EOR of high viscosity common heavy oil reservoirs, and it can provide a new technical route and on-site basis for enhancing oil recovery in this type of reservoirs.