Climate variability and human activities are two main factors influencing hydrological processes. For more reasonable water management, understanding and quantifying the contributions of the two factors to runoff change is a prerequisite. In this paper, the Budyko decomposition hypothesis and the geometric approach were employed to quantify climate change and human activities on mean annual runoff (MAR) in six sub-basins of Luanhe river basin. We split a long-term period (1956–2011) into two sub-periods (pre-change and post-change periods) to quantify the change over time. Observations show that annual runoff has had a decreasing trend during the past 56 years in the Luanhe river basin. Based on a geometric approach, the climate impacts in these six sub-basins were 7–49%, and the contributions of human activities were 51–93%, approximately. According to the Budyko decomposition method, impacts of climate variation accounted for 15–40% of the runoff decrease, and the contribution of human activities was 60–85%. Both methods were simple to understand, and it is feasible to separate the climatic- and human-induced impacts on MAR. This study could provide significant information for water resources managers.