Based on 67 years of monitoring hydrometeorological factors,including river flow, precipitation, evaporation, water level and outflow of Erhai Lake from 1956 to 2022, the natural water resources of Erhai Lake were calculated using hydrological analogy and water balance methods, the trend and periodicity of natural water resources in Erhai Lake have been investigated using the Manner-Kendall method and Morlet wavelet analysis method, and the factorsthat impact Erhai Lake's water resources, including precipitation, evaporation,and human activities. (2)The natural water resources of Erhai Lake exhibit asignificant decreasing trend over time, with an average decrease of 52 millioncubic meters every decade. The Mann-Kendall method was employed tocalculate that the annual water resources display a significant downward trendover time, while the water resources in the four seasons only show a significantincreasing trend over time.(3) Wavelet analysis and calculations reveal periodicvariations in seawater resources in Er over the past 67 years at different scales,which significantly influence the trends of abundant and dry seawater resourcesin Er. The first major cycle occurs approximately every 53 years, followed by asecond major period of around 41 years. Additionally, there is a third main periodof about 30 years, while the fourth and fifth main periods occur approximatelyevery 9 and 12 years respectively.(4) Through correlation analysis of precipitation,evaporation, human activities and other factors affecting the amount of seawaterresources in Erhai Lake, it was observed that the changing trend and fluctuationperiod of annual precipitation in the Erhai Lake basin are positively correlatedwith those of annual water resources. The annual evaporation is sometimespositively correlated with the annual water resources, and sometimes negativelycorrelated, indicating that the annual evaporation has a variety of combinationson the annual water resources in Erhai Lake. The population and waterconsumption in the Erhai Lake Basin have been steadily increasing with theprogress of human society, while human activities continue to exert a profoundimpact on the underlying surface conditions. The current decline in seawaterresources in Erhai Lake is the result of a combination of precipitation and humanactivities. Initially, the impact of reduced precipitation outweighs that of humanactivities, but subsequently, the influence of human activities becomes moresignificant than that of precipitation.