The evolution process of blackout caused by ice disaster can be divided into four stages:ice and snow leading to freezing rain，freezing rain leading to transmission line icing，transmission line icing leading to power grid fault，and cascading failure leading to blackout.The way freezing rain affects transmission line fault probability involves the meteorological law of sleet forming，the thermodynamics law of transmission line icing，and the mechanical law of transmission line broken and tower collapse.Therefore，the information needed for online evaluation of blackout risk due to freezing rain is summed up first.Then，the ice thickness covered on the transmission line is calculated using weather forecast and micromorphology information.And the online transmission line fault probability，which can be used to update the envisioned fault table of the security stability analysis software，is evaluated using real-time line monitoring information.An early-warning model for blackout due to ice disaster is established finally based on the electrical law of flow transfer and dynamic law of system crash.