In order to improve the condition that a certain deviation of a
lightning trip-out rate exists between
lightning current amplitude probability distribution functions recommended by regulations and the IEEE (Institute of Electrical and Electronic Engineers) and practical
lightning current amplitude probability distribution, the invention discloses a piecewise fitting method of a lightning
current amplitude probability
distribution function. According to the method, a numerical
analysis method is adopted to perform piecewise fitting on the lightning current amplitude probability
distribution function, continuity correction is performed, and a curve of the lightning current amplitude probability
distribution function, which is obtained in the way, is strongly relevant to a practical lightning current amplitude
probability curve. As is well-known, the lightning current amplitude probability distribution function is an important calculating parameter for calculating the lightning trip-out rate of an electric
transmission line, and the accuracy of a value directly influences the accuracy of a calculating result of the lightning trip-out rate. Therefore, by using the fitting method disclosed by the invention, the more accurate lightning trip-out rate can be obtained, and operation reference is supplied to the department of
electric power operation for designating a lightning protection weak area of a
regional power grid.