The invention provides a transmission line mountain fire spread warning method with the combination of public network weather. The method comprises a step of obtaining a fire point coordinate, a step of calculating the spread speed of a fire point spread direction based on the fire point coordinate, a step of calculating the linear position of the fire point in the spread direction after a spread time according to the spread speed, and obtaining a spread coordinate, a step of calculating the spread area of the fire point according to the spread coordinate, a step of carrying out warning level definition on the transmission line in the spread area according to the spread time and issuing warning. According to the method, an effective information support is provided for the judgment of a grid mountain fire disaster by a power department, the mountain fire spread speed from the fire point to the transmission line can be calculated, the warning level of the transmission line is judged through time according to the mountain fire spread speed, and the method has high accuracy and practicability and plays an important role in maintaining security and stability of a grid and reducing a disaster loss.