65 years, 83 years, 84 years, 86 years and 87 years annual rainfall data from 10 raingauge stations in Eastern India were analysed following conventional method, ARIMA ( autoregressive integrated moving average) model, and polynomial regression for assessment of the occurrence of drought and flood periods. It was found that the present annual rainfall condition may be represented by first and second methods, while polynomial regression may represent a few years in the present condition. It was also found that the mean values of the mean interval of two consecutive drought years, mean interval of two consecutive flood years, and mean interval of consecutive drought and flood years were worked out to be 8.244 years, 6.690 years, and 3.489 years respectively.