The simulation analysis on floods and droughts and research on their influences are hot topics in the study on regularity of climate events. The calculation of flood and drought periods and the detection of sudden changes are important approaches in exploring the regularity. Based on the historical data of flood-drought grades in the past 540 years, the flood and drought periods and the sudden changes are calculated by means of power spectrum, wavelet analysis, index analysis and Mann-Kendall method. The results showed that the floods and droughts of Haihe river basin took predominance for 10, 23, 37, and 75 years in the history with a transformation from drought to flood in the 17th to the 18th century.