Abstract—For the reason that seldom research has been studied on the lightning trip flashover rate (LTFR) of distribution line, this paper focus on studying the calculation method about LTFR. The distribution line without mounting grounding line, flashover is mainly caused by direct stroke lightning and induced stroke lightning. Then, a conclusion can be drawn that LTFR is made up of direct stroke lightning trip rate and induced stroke lightning trip rate. Based on these, a model which can consider the structure of the distribution network, the type of grounding and lighting withstand level (LWL) is established. Furthermore, ATP-EMTP and the mirror method is applied to calculate the flashover probability caused by direct stroke lightning and the induced stroke lightning respectively. Moreover, to check the accuracy of the model, a typical 10kV distribution line in high lighting stroke area of China which is called Gaotian Line is chosen and the LTFR of the line is computed as well. The result shows that the computed result is very close to the practical running result, which proves the correctness of the model.