The design standards of port breakwaters are generally determined by calculating the extreme values of waves,but the calculation of extremes has a certain degree of uncertainty.To clearly understand and grasp of the uncertainty of the calculation results,the influences of three factors,namely observation errors,data volume and calculation models,on the calculation results are analyzed.Based on the Monte Carlo method,stochastic samples are generated to simulate these three factors,corresponding to the physical uncertainty,statistical uncertainty,and model uncertainty in the extreme wave calculation.The results show that the greater the physical uncertainty,the more unstable the extreme wave calculation results are and there is a slight increasing trend,and the impact on short return period extreme waves is greater.Moreover,a larger sample size has smaller statistical uncertainty and has a greater impact on long return period extreme waves.For short return periods,the Pearson-III distribution has smaller model uncertainty,and for long return periods,the Weibull distribution has smaller model uncertainty.