To study the hydrological effects of human activity in the Sanjiang plain, the influence of human activity on surface runoff processes, soil water content，groundwater level, and water quality are analyzed. Then, the spatial-temporal scale and the trend of hydrological effects of human activities are discussed. Results suggest that hydrological effects of human activities will expand on both temporal and spatial scales. More specifically, the intense influence of human activities on runoff processes, reticular development of the regional water system, fragmentation of wetlands，deterioration of water quality and so on will continue for a long time. The impacts will become more and more serious, and should be paid adequate attention.