本文分析了发输电组合系统主要可靠性指标，如：LOLP、LOLF和EENS，随系统负荷的变化规律，以拟合的规律曲线连续、光滑等为目标，建立系统可靠性指标随系统负荷变化的三次样条插值模型。通过插值边界条件、插值点导数等信息，即可求解该模型。结合该模型，可建立电力系统可靠性预测估计模型，以避免负荷变化时可靠性的重复评估。将该模型应用于RBTS测试系统。算例表明：系统可靠性随负荷呈非线性的变化规律；当负荷变化时，可直接应用该模型预测估计系统可靠性，其平均绝对百分误差约2.0%。 The rules between the reliability indices of generation and transmission system, such as: LOLP (loss of load probability), LOLF (loss of load frequency), EENS (expected energy not supplied), and the system load are analyzed. The relationship model between the power system reliability and system load rate is modeled using cubic spline interpolation, and the model can be solved according to the interpolation boundary conditions, the interpolation points and derivative information. Therefore, a fast evaluation technique based on the proposed model for the reliability of power systems can be obtained, which can avoid the duplication of reliability evaluation with multi-load levels. The proposed model is applied to the RBTS system. Results indicate that the relationship between the system reliability and load rate is non-linear variation. The average error for the evaluation on the reliability in these cases is about 2.0% when the load changes.