When a typhoon transits a region, the accidents of line breakage and tower collapse often occur due to the large wind force, so it is one of the natural disasters which are the most threat to operational reliability of transmission lines in coastal areas. Because of the high risk of typhoon disaster, establishing a typhoon early warning system is more economical and efficient to enhance the ability of power grid to withstand typhoon disasters. The existing typhoon risk early warning method for power grid uses the regional forecasting wind speed provided by the meteorological agency directly, which does not take the influence of micro-terrain around specific line on the wind speed into account, thus the missed alarm and false alarm are easy to appear. Therefore, a typhoon risk early warning method for power transmission line considering micro-terrain correction is proposed in this paper. The warning area is divided into 0.01°×0.01° grids by longitude and latitude in this method, and transmission equipment in each grid is associated with the microclimate information and micro-terrain information of the grid. The calculation method of correction factor of wind speed for transmission line under micro-terrain conditions is set up, in order to identify the set of lines that may suffer from typhoon disaster more accurately, and early warning is conducted according to risk level. The feasibility of this method is proved by an instance.