Water resource is now a serious problem around the world due to the impact of climate change and increasing human activities. There are serious concerns about the impacts of climate change on water resources. Water resource problem is particularly prominent in semi-arid and arid regions since the water resources and primarily runoff in these regions are highly sensitive to climate change; and a small change of climate variables may result in significant variation of hydrological cycle and subsequently change the regional water resource. With a channel of 2309 km and a basin of 5.57*105 km2, the Songhua River is located in the northeast of China where the latitude is high and the climate is cold. Natural runoff as the main source of surface water plays an important role in agricultural irrigation, socio- economic development,hydropower generation, wetland recharge and local eco-environmental conservation in the basin. However, the runoff in the whole river basin has experienced dramatic change in the last decades. It is necessary to study the trend of the runoff change and to quantify the influencing factors of the runoff change on different spatial scales. Based on annually observed hydrological data at six gauge stations on the Songhua River mainstream and annual precipitation at 62 meteorological station in and around the Songhua river basin, the changes of annual runoff and the contributions of the major influencing factors to them during the period 1955- 2010 were analyzed. First, the cumulative anomaly and sequential cluster were used to detect the abrupt changes of each runoff series. Three inflexion years were detected that divided the entire time period into four periods(increasing- decreasing- increasing- decreasing) for each gauge station.Without considering the effect of evapotranspiration, the slope change ratio of cumulative quantity(SCRCQ) was adopted to estimate the impacts of precipitation and human activities. The result shows that the contribution of precipitation was 26%- 35%, 0.1%- 10% and 25%- 43%, respectively, while that of human activities was 65%- 74%, 90%- 99.9% and 57%- 75% respectively for the different periods compared with the baseline period. It is obvious that the human activities are the most important factor to runoff change. While the impact of human activities on runoff change is still increasing in most basins of china, that of the 4th period in the Songhua River basin was less than the 3th periods. However, the effect of human impacts was still greater than that of precipitation. Considering the severe stress of water resource, anthropogenic impact on runoff changes should be given more attention in future.