In deltas, the flood-tide coupling mechanism in tidal rivers changes under the impact of the climate change. Apart from the magnitude of high water level, the timing and its seasonality are also important factors that can reflect the varied flood regime. This research has adeopted a directional statistics methodology, and generated the characteristics of high water level seasonality, i.e., the concentraction time, ratio, period as well as the their changing patterns over the decades. The Pearl River Delta has been set as the study area, and the recording high water level along with the timing of 16 hydrological stations have been studied. The results show that: (1) there is no significant difference in the seasonality calculated by the circular distribution method with the magnitude of water level is considered; (2) the high water level concentration period of both outlet and income stations are longer than that of the river net; (3) the concentration date of outlet stations are similar to river net, and previous to that of income stations; the delay in the concentration time becomes statble around the whole Pearl River Delta; (4) the fluctuation of concentration date is stronger in the oulet and income stations than the river network, but the fluctuation becomes slight during the last four decades. The study provides a new perspective in analyzing delta flood variation, and a theoretical base for the sampling and frequency analysis of the high water level. It can serve as a theoretical support for making the regional flood protection policies.