Abstract: This paper describes the viscosity changing rule and influencing factors of xanhan gum solution in pilot test in GuDong oilfield, further compares them with the change of viscosity of partially hydrolyzed polyacrylamide(PHPA) solutlon in polymer flooding test. In result, xanhan gum is better than PHPA in terms of viscosity increasing, salt tolerant property, shearing Strength, thermal stability and so on. It is hardly affected by shearing force and polluted water during injection. In addition, it can be injected by a relatively simple site injecting system. Therefore, it is suitable for implementing EOR in oilfields with poor conditions and absent of pure water.