Abstract: Environmental change has altered the river hydrological health regimes, and consequently affected the ecological health of river. Therefore, it is essential to develop a method to quantitatively analyze the attribution of river hydrological health evolution. This study selected the typical semi-arid Laohahe River basin in Northern China as a case study area. Observation data were obtained from 3 hydrological stations, 17 rain gauge station and 6 meteorological stations in the study area. Firstly, the natural streamflow series from 1964 to 2016 was reconstructed using the observations and the Variable Infiltration Capacity (VIC) model. After that, the level of river hydrological health (H) was assessed based on the ecological flow threshold, which was calculated by probability density curve. Finally, the 'simulated-observed' comparison method was adapted to quantify the effect of climate changes and human activities on the river hydrological health. Results showed that human activities were the major factors that have caused river hydrological health deterioration since 1980 in Dianzi and Taipingzhuang sub-basins, which accounted for 86.9% and 87.9%, respectively. Widespread agricultural irrigation and reservoir operation were the two crucial reasons that caused the alterations of natural hydrological regime, which further led to the river ecological destruction over Laohahe River basin. Whereas, increasing rainfall in 1990s had a significant effect on maintaining river hydrological health because the large amount of rainfall helped reduce the human activities influence. The case study demonstrates that the attribution of river hydrological health evolution can be quantitatively described based on ecological-flow threshold and 'simulated-observed' comparison method, which will provide scientific basis for river ecology protection and water resource management under changing environment.