Polymer flooding was an effective way in Enhanced Oil Recovery and has been applied in complex reservoirs such as offshore field. Polymer pilot test had been implemented to Bohai field which is the largest offshore field in China. It is necessary to estimate the risk of implementation of polymer flooding in offshore field due to the fact that the offshore operation is much more difficult and the cost is much higher than the onshore. Current method of risk evaluation for the polymer flooding can only be applied to one parameter so that it would underestimate the uncertainty of the prediction. Thus, we proposed a potential risk appraisal method in polymer flooding based on the Monte Carlo principle and inverse distance weighted method. Through determining the random distribution of the influencing parameters in polymer flooding and by means of stochastic simulation and statistical analysis, the potential appraisal index and risk index of polymer flooding were predicted. The result of example in Bohai field indicated that not only the probability distribution of technical index (EOR) and economic index (IRR) in polymer flooding were predicted but also the confidence intervals and expectations of these prediction indexes were obtained. As a result, the polymer flooding risk was quantitatively characterized through the risk index and the evaluation is more reasonable and comprehensive than the evaluation with other method. Also, the method could be used for the other EOR technology.