Quantifying the impact of the streamflow forecast uncertainty on the short-term (referring to the next day) power generation operation of a cascade hydropower system is more complex than a single reservoir but important, due to the compensation effect between upstream and downstream reservoirs within a cascade. In this paper, we propose a short-term cascade hydropower stations optimal operation model based on conditional value-at-risk (called the CVaR-SCHOM model) to guide the actual power generation using uncertain streamflow forecast. We first analyze the uncertainty of short-term streamflow forecasts and establish the conditional probability function to describe the uncertainty of the forecasted streamflow sequence. We next propose the short-term operation target of the cascade hydropower station at the greatest expected benefit. We then introduce the conditional value-at-risk theory to analyze the risk of power shortage in different operating schemes under a certain level of confidence. Finally, based on the risk attitude of the decision-makers, we balance the benefit and risk of cascade hydropower stations operation and establish the CVaR-SCHOM model. We verify the model using the Jinguan cascade hydropower stations in the Yalung River basin. The main contributions are as follows. 1) By using k-means clustering to classify the forecasted streamflow sequence into different magnitudes and then using the joint probability function of the relative errors, an accurate description of the uncertainty of the short-term streamflow forecast can be achieved. 2) The internal characteristics of each cascade power station and the interrelationships between the cascade hydropower stations are complicated, and the power deviation and forecast error can show positive or negative correlations. 3) Compared with the traditional deterministic optimization model, the CVaR-SCHOM proposed in this paper performs well in real-world applications. The proposed model yields different degrees of improvement of the benefits and risks for various forecast magnitudes. The decision-makers can choose different schemes according to their risk attitudes.