Due to the impact of climate change and human activities, the upper and middle reaches of the Tao'er River have become an ecologically sensitive area in Northeast China. It is important to evaluate the contributions of climate change and human activities to water suitability in the Tao'er River area. From the perspective of water and heat balance, the water suitability index (c_r) was used to analyze the water suitability of the upper and middle reaches of the river. The nonparametric Mann-Kendall, moving t-test and cumulative anomaly methods were used to detect abrupt changes in Taonan station runoff from 1961 to 2012. Three inflexion years were detected. Thus, the entire time period was divided into four periods: 1961–1974, 1975–1983, 1984–1998, and 1999–2012. In order to estimate the impacts of climate change and human activities on runoff, the slope change ratio of cumulative quantity (SCRCQ) was adopted. Finally, the contribution of climate change and human activity to c_r was transformed from the contribution of climate change and human activity to runoff by the sensitivity coefficient method and SCRCQ method. The results showed that the water suitability index (c_r) had a decreasing trend 1961–2012. Factors influencing cr, such as net radiation and runoff, also exhibited a decreasing trend, while precipitation exhibited an increasing trend over the past 52 years. The trends of cr, net radiation and runoff were obvious, which passed the Mann-kendall test of significance at α=0.05. Human activities were the main factors that affected runoff, although the degree of impact was different at different times. During the past 52 years, the biggest contributor to the change in c_r was precipitation.