The invention relates to a lightning arrester reserve part reserve method and system. The lightning arrester reserve part reserve method comprises the following steps: reading lightning arrester information from a direct current power transmission system simulation model; inputting the lightning arrester information into a preset probability estimating model to obtain lightning arrester fault probability; determining probability that the number of fault lightning arresters is greater than n according to the lightning arrester fault probability, wherein the n is an nonnegative integer; and determining the number of the lightning arrester reserve parts according to the probability that the number of fault lightning arresters is greater than n, and reserving the lightning arrester reserve parts according to the number of the lightning arrester reserve parts. According to the lightning arrester reserve part reserve method and system, the number of the lightning arrester reserve parts can be flexibly determined according to the corresponding valve block fault rates so as to provide relatively accurate reference for the reservation of the lightning arrester reserve parts and to improve the accuracy of the reserved lightning arrester reserve parts.