Abstract: Due to the influence of climate change and human activities, it is difficult to meet the consistency assumption in time series frequency calculation of hydrological elements.Therefore, it is need to figure out a calculation method for inconsistent hydrological series.In this paper, the hydrological data of Cuntan station, with a long station construction history, were collected for the hydrological frequency calculation and analysis of long series.Regression analysis and Mann-Kendall method were used for trend analysis, and sliding T test and Lee-Heghinian method were used for mutation test.In order to explore the application effects of different methods, two methods were adopted, one was frequency calculation after correction of inconsistent series and the other was frequency calculation based on inconsistent series.The results showed that both methods could improve the reliability of frequency calculation.For the sequence with large sample size, two methods have the same application effect.When samplesize was small, the correction method was more practical but the improvement degree was limited, and the representativeness of the data also had a significant impact on the calculation results.In practice, we should enlarge the sample capacity as much as possible, improve the representativeness of the data and modify the consistency of series with a trend.