Wildfire disasters on overhead transmission lines seriously threaten the safe and stable operation of large power grids and the normal use of electricity. After a wildfire occurs near a transmission line, it is often inefficient to take measures afterward. In order to guide the early warning of wildfire disasters on overhead transmission lines and strengthen the active prevention of them, this paper proposes a method for calculating the occurrence risk of overhead transmission line wildfires that considers the hazards of vegetation burning. Compared with conventional methods, the considerations are more comprehensive. A calculation method for wildfire trip risk coefficient based on tripping probability and transmission load that does not need to calculate the wildfire spread process is proposed, and the calculation is simpler. For the first time, a comprehensive calculation method for the whole-process tripping risk of overhead transmission lines caused by wildfires combined with the wildfire occurrence risk and the trip risk coefficient is proposed, compared with methods that calculated only the risk level of wildfires and ones that calculated only the tripping probability, comprehensively analyzing the entire process from the potential factors of wildfires to the danger of tripping, which is more scientific. Application cases showed that this method accurately reflected the risk of wildfire trips on overhead transmission lines, thereby guiding the optimization of the wildfire prevention resource deployment in advance and improving wildfire prevention in power grids.