Research on the periodic characteristics of the runoff evolution in the Lower Yellow River is of great importance for flood control, beach regulation and water resources utilization in the Lower Yellow River. By using wavelets to conduct scale analysis of runoff series, the periodic change rule of runoff series on different scales can be obtained. By using the maximum entropy spectrum to analyze the spectrum of runoff, the main period of runoff sequence can be obtained. In this paper, these two methods are applied to the annual runoff of the Lower Yellow River. The results show that: the annual runoff in the Lower Yellow River has multi-scale change law; the four stations have the same main period; there are differences in periodicity between stations, as the catchment area increases, the quasi-periodic value decreases, and the periodic fluctuation becomes more obvious; after 2018, the annual runoff of the Lower Yellow River will be in the dry season. Furthermore, the study can reveal the change law of runoff sequence in the Lower Yellow River to a certain extent, and provide a theoretical basis for river management.