Changes of flood series vary among different seasons. This research developed a flood frequency analysis method based on nonstationary seasonal maximum peak flow. Taking upstream of Wujiang River (UWR) as our study area

seasonal extremes were drawn according to three seasons: dry season (DS) from Nov. to Feb.

season of frontal rain (SFR) from Mar. to Jun. and season of typhoon rain (STR) from Jul to Oct. The influences of different seasons on the results of flood frequency analysis were also studied. The results show that: ① Statistical characteristics of different seasons vary in UWR. Mean and contribution to AMS(annual maximum series) （2.22%）of DS are both the lowest while that of SFR are the highest. Standard deviation of STR is the highest. ② All the seasonal series (SS) have ascending trends. Change of SFR causes the most influence on design flood

but the influence is descending. Variation of STR expands the deviation between design floods of different return periods

and the influence is increasing. ③ Design flood from non-stationary flood frequency analysis were larger than the one from traditional method. The one based on SS is larger than AMS

and the difference between increases along with the return period

which is more than 1000 m

3

/s when return period is 100 years.