Abstract: Based on annual maximum water level (AMWL) data obtained from 34 gauging stations in the Pearl River delta (PRD) and the oceanic Nino index (ONI) data in the Nino 3.4 region from 1951 to 2008, the GEV distribution model is used to get the flood frequency analysis of AMWL. In order to comprehensively understand the water level fluctuations characteristics in the delta, the water level variation corresponding to different flood frequencies calculated from a series of pre 1980 and post 1980 years are examined. The studies of interdecadal variations in the response of the flood water level to ENSO in the past fifty years have been carried out by using moving correlation. The space time variations in the flood water levels corresponding to different return periods in the PRD region suggest that the flood water level increases gradually from the coastal areas to the riverine system. The flood frequency variations have shown that the most serious flood risk is in the coastal region because this region is extremely vulnerable to the flood hazards. The flood water level increments corresponding to different increments of the flood periods in all 34 sites are great. In the upper PRD, the flood water levels show a decreasing trend while there is an increasing trend in the middle and lower PRD. The long term variation of interannual relationships between ENSO and the flood water level has a significant stage characteristic and has a great change in the 1980s. Before and after the abrupt change, the correlation coefficients have remarkable differences. The flood water levels have various responses to various seasonal ENSO events.