Abstract: In order to reveal the evolution characteristics of Dagu River runoff into sea and the main driving factors, Mann-Kendall test and modified Mann-Kendall test, the cumulative departure method and Moving t-test, Morlet continuous complex wavelet analysis were employed to study the Dagu River runoff during 1956 to 2016 and its changing trend, mutation characteristics and variation period. The contribution rates of climate change and human activities to the change of Dagu River runoff were quantitatively calculated by using the rainfall-runoff double cumulative curve. The results showed that the Dagu River runoff showed a significant decreasing trend, with an average decrease rate of 15.85 million m3/a. In 1976, a sudden change occurred from more to less, and the main period of change was 21 years. Human activities were the main factor leading to the reduction of Dagu River runoff, and large-scale water resources development activities have changed the process of water resources transformation in the Dagu River Basin. The research results can provide reference for the development, utilization and protection of water resources in Jiaozhou Bay and the evaluation of ecological environment.