Based on hydrological data from the 4 stations on the Beijiang main stream, the annual maximum peak flow series were constructed in this paper. The linear regression, Mann-Kendall (M-K) methods, empirical mode decomposition (EMD) and rescaled range analysis (R/S) were used to find out the variation law of the series and the linear correlation was used to analyze the impact factors preliminarily. The results show that there is insignificant change trend in the series, and there exists abruptly jumping points. But all the series have the fluctuating cy - cles of 4 to 6 a and 8 to 10 a. The series for the 4 stations all get long-term memory characteristics so that the future tendency of the series is indistinctive. The result of the linear correlation shows that South Asian summer monsoon is the main factor to the series and sunspot may affect the cycle of the series.