Abstract: To effectively implement early warning of natural disaster risk for power grid and furthest reduce the affect of natural disaster on power grid, a block chain technology based power grid disaster early warning and decision making system was researched. Firstly, according to the coupling relationship between power grid and natural disaster, the information resource such as the data collected by power grid intelligent devices and natural meteorological information and so on were mined to construct the overall architecture of power grid disaster early warning and decision making system supported by block chain. Secondly, taking the ice disaster occurred in power grid for example, according to weather forecast, microtopography information and so on and by use of model prediction control (MPC) algorithm the ice-coated model of power network transmission line was revised, and the probabilistic model of transmission line fault caused by overweight of ice-coating, transmission lines galloping and insulator flashover was established. Finally, the early warning model of ice-coated transmission line was solved by MPC algorithm to realize the early warning of transmission line. Taking several 220 kV transmission lines located in the central and north-west regions of a certain city for example, the predicted analysis on ice-coating was carried out, and the feasibility and effectiveness of utilizing the proposed block chain based power grid disaster early warning and decision making system for the forecasting of the ice-coated thickness on transmission line are verified.