Using main meteorological and eco-environmental observational data in the Yellow River important water source supply area of Gannan Plateau,the climatic change characteristics and eco-environmental effects of this study area were analyzed. The results show that the interannual variation of precipitation tended to decrease, and the variability is -22.6~-9.6 mm/10a.In the 1980s the sudden change phenomenon in precipitation took place, in addition the 6~7a and 15a main periods of oscillation exist in most parts of the study area; temperature displays a remarkable increasing trend with an increasing rate higher than that of the whole country, in terms of seasonal changes, the increasing rate of winter is higher than that of the other seasons, in the 1970s the sudden change phenomenon in temperature took place with a persistent ascendant trend after 1980; water resource shows a significant descendant trend, the valley precipitation presents a remarkable positive correlation with the water resource, and the valley drought index presents a remarkable negative correlation with the water resource, the decreasing precipitation and increasing drought index result in a decrease in water resource; theoretically the domestic animal capacity of the regional savageness grassland is 428.82 ten thousand sheep, but in fact the over loading rate reaches 96.39%; climate changes is the natural factor for plain ecological degradation, but overgrazing, excessive tree felling and grass cutting, artificial destruction, biological chain unbalance and so on are the artificial factors for plain ecological degradation, water resource sharp decrease, diversity of biology decrease and eco-environment degradation are the combined effects of the above two factors in the Yellow River important water source supply area of Gannan Plateau.