Due to the need for pre-disaster prediction and rapid post-disaster estimation of disaster situations during the “Dragon Boat Water” period (from late May to mid-June) in Guangdong, the integrated disaster index (IDI) of “Dragon Boat Water” is calculated in this study, by using rainfall, heavy rainfall flood disaster data during the “Dragon Boat Water” period in Guangdong spanning from 1995 to 2021. Then, IDI is classified into light, medium, and heavy levels, employing the quantile method. The study focuses on analysing disaster features and the relationship between rainfall and disaster situations. The key results are as follows: To begin with, the years 2005 to 2010 are the peak of rainfall intensity, rainfall range, heavy rainfall frequency, and duration of the Guangdong “Dragon Boat Water” from 1995 to 2021. The peak of disaster intensity is in 2005-2008. The two peak intervals are relatively consistent. Following 2008, the heaviest disaster situation year, there is a downward tendency in integrated disaster intensity. Over the past decade (from 2012 to 2021), all five kinds of disasters also show a downward tendency. The number of collapsed buildings, the number of affected people, and affected crop areas show the most pronounced reductions, while direct economic losses display a more moderate decrease. Furthermore, the correlation between affected crop areas and rainfall factors is the highest, followed by the number of affected people and direct economic losses. The levels of integrated disaster and direct economic losses are primarily affected by the intensity of rainfall and the frequency of heavy rainfall. Meanwhile, the number of affected people and affected crop areas are primarily influenced by both the intensity and range of rainfall. The number of collapsed buildings and the number of deaths are mainly influenced by the frequency of heavy rainfall. Lastly, the established fitting equation between the average total rainfall and disaster of “Dragon Boat Water” shows reliability, by estimating the integrated disaster level and disaster situation data of “Dragon Boat Water” approximate to the actual disaster situations. The hit rate of estimates for integrated disaster level is 59%, and the hit rates for estimates of heavy, medium, and light levels are 20%, 50% and 78.5% respectively. The estimates of a heavy integrated disaster level are slightly lighter than the actual situation, the estimates of the medium level are consistent or slightly lighter, and the estimates of light level are basically consistent. Applying the meteorological disaster risk assessment method in this study, the disaster level and various disaster data can be quantitatively estimated in advance based on rainfall prediction of the “Dragon Boat Water” period. thereby providing a reference for emergency management departments in disaster prevention and reduction.