The icing of power lines can severely endanger the operational safety of the power system. Solar radiation is a crucial heat source for the thermal balance of iced-over transmission lines and should not be overlooked. Transmission line radiation reception is affected by various factors, such as topography, environmental shading, and line orientation. Therefore, a different calculation method from that used for ground radiation needs to be applied. To evaluate variances in solar heat radiation received by transmission lines oriented differently within an area, especially in mountainous areas, This paper introduces a method to generate a grid-based distribution map of radiative heat for transmission lines, utilizing digital elevation models (DEM). The transmission line orientations are gridded along latitude and longitude. This method constructs the three-dimensional spatial position using the solar angle of incidence and grid units. It computes the cumulative radiant heat absorbed per unit distance of the transmission line at a certain height above the ground on a specific day of the year. Considering terrain shading effects. It also provides a method to calculate transmission line orientations based on latitude and longitude units. This approach for plotting transmission line solar radiation maps effectively estimates the impact of solar radiation variations on the thermal balance of iced-over transmission lines in areas with topography features, also including aspects such as line droop that pertain to solar heat sources in the design of transmission lines, thus offering valuable insights for the planning of high-voltage transmission lines.