The invention provides a method for calculating thunderbolt density, which is used for calculating the thunderbolt density in a studying area and drawing a corresponding thunderbolt density distribution graph. The method comprises the following steps: firstly, extracting parameters related to thunderbolt information from original data, and removing error data in the original data; secondly, setting size of grids of the thunderbolt density distribution graph, dividing the studying area according to the size of the grids, and relating the grids to the area corresponding to the grids; thirdly, calculating the thunderbolt frequency of the area corresponding to each grid in a certain period of time; fourthly, calculating the thunderbolt density of the area corresponding to each grid; fifthly, performing data processing, wherein classification and partition are carried out according to the strength of the thunderbolt density, and a boundary value is rounded; and finally, drawing the thunderbolt density distribution graph according to the result of the data processing. The method for calculating the thunderbolt density can obtain the thunderbolt density distribution of the studying area by processing the data of a thunderbolt positioning system so as to guide the thunderbolt prevention in the area.