Qinghai Lake, as the largest saline inland lake in China, plays an important role in the surrounding semi-arid ecosystem. In recent years, the lake water level has increased rapidly; however, the driving factors causing water body changes are not fully understood. This study aims to investigate the hydrological processes in Qinghai Lake from 1959 to 2016, and to discuss their possible linkages to climatic change and human activity. The results indicate that both the water level and lake area gradually declined to their minima in 2004, before increasing rapidly. Annual evaporation and total runoff vary widely, but have shown an overall shift from decreasing to increasing trends. The annual average temperature has followed an increasing trend, and annual precipitation has increased rapidly since 2004. Hydrological changes (water level and lake) are positively correlated with runoff inflow into the lake and negatively correlated with evaporation from the lake surface. The water body expansion in recent years can be attributed to the decreasing difference between precipitation/river runoff and evaporation. The total water consumption by human activities has had a limited contribution to the water body changes. We conclude that hydrological changes have depended more on climatic variations than on human activities.