The invention provides a power grid reliability horizontal determination method based on a static-state reliability probability index. According to the invention, by considering factors of probability of stopping of an element, uncertainty in an operation environment, risks caused by multiple constrains and the like, reliability indexes of the element, a load point and a system can be calculated. A specific load shedding node and load shedding quantity are recorded, and the judgment criteria for determining the power grid reliability level is given, so comprehensive and objective evaluation is performed on the static state reliability of the power grid and the reliability level of the power grid can be determined. Thus, the power grid reliability horizontal determination method based on the static-state reliability probability index has the effective actual guidance meaning and application value.