Abstract: By use of the actual monthly run-off data kept by Zipingpu hydrometricalstation, a wavelet analysis is made for the time series of the upstream run-off in the Minjiang River by season. The results show a periodical change in terms of a few dimensions concerning the time series in middle and upperstream run-offs in the Minjiang River. The strongest oscillation energy for the four seasons is observed when the primary period is at 16a, 2.5a, 11a and 18.5a respectively and the primary period of the run-offs is basically distributed at a relatively smaller temporal dimension.