River ecological droughts in the middle and lower reaches of the Yellow River are becoming increasingly severe, posing significant challenges to water resources management and ecological protection in the region. To assess the river ecological drought conditions, this study calculates the ecological water demand at six hydrological stations in the research area using the Tennant method, Qp method, minimum monthly average flow method, and annual distribution method. Additionally, the standardized river ecological drought index (REDI) is constructed to evaluate the ecological drought status of the rivers. Furthermore, the study employs Kendall trend analysis, M-K abrupt change test, and Morlet wavelet analysis to investigate the evolution characteristics of drought across multiple time scales in the watershed. The results indicate that the degree of ecological drought at various hydrological stations generally shows a significant intensifying trend on the annual scale, so does that on the seasonal scale, except for a few seasons in different stations. The years of drought abrupt change on the annual scale mainly distribute in the 1970s and 1980s, while those on the seasonal scale vary by stations. There is a significant difference in the first principal period of the river ecological drought index between annual and seasonal scales.