Historical flood usually comes from investigation and textual research，with errors.How to evaluate the influence of historical flood error on design flood calculation results is of great significance.Existing studies usually only consider the single effect of magnitude or recurrence period，but the combined effect of magnitude and recurrence period error is rarely studied.In this paper，P-III/LM flood frequency calculation model is built based on P-III distribution and L-moment method（LM）.Historical floods of different orders of magnitude，different recurrence periods and combined disturbance of magnitude and recurrence period are added on the basis of measured data to study the influence of historical flood error on design flood.The application results of Ganjiang Dongbei hydrological station show that the influence of historical flood magnitude error on design flood is more significant than that of current period error.Magnitude and recurrence interval there is interaction relationship，when disturbance level and return period that not only has positive effect，and negative offset weakening，in magnitude and recurrence interval joint disturbance-20%～20%of cases，once，once in 1000 and 2000 in 100，a flood design value maximum deviation ratio were 9.12%，8.53%，6.20%and 5.86%，5.50%，4.02%.Large or small error of 20%in the recurrence period can roughly offset the impact of large or small error of 10%.