This paper analyses the relations of forecasting result using wavelet periodic analysis model with the length of runoff series、time interval as well as the drainage basin scale from a typical reservoir inflow runoff forecasting example.The initial conclusions can be gotten as follows: ①The length of time series should neither be too long nor too short in the wavelet periodic analysis model.Because when the length of time series exceeds a certain limit

the forecasting result of the model will have no further improvement;②Through the contrast between month and range time interval

we can get that when time interval becomes short

the singularity of runoff series would become more salience

and the forecasting result of the model becomes worse;③The wavelet periodic analysis model is sensitive to the basin scale.The smaller the basin area is

the more irregular the runoff series change

as a result

the forecasting result of the model is worse.