The invention relates to a symmetric single-pole flexible direct-current engineering convertor station insulation coordination method and system. The method comprises the following steps: arranging aplurality of lightning arresters on a main wire of an existing symmetric single-pole flexible direct-current engineering convertor station, wherein the lightning arresters comprise a connection transformer valve side lightning arrester, a bridge arm reactance valve side lightning arrester, a bridge arm reactance inter-terminal lightning arrester, a direct-current pole bus lightning arrester, a direct-current circuit lightning arrester and a connection transformer valve side neutral point lightning arrester; and determining characteristic parameters of the various lightning arresters to implement insulation coordination of the symmetric single-pole flexible direct-current engineering convertor station. Insulation coordination of the symmetric single-pole flexible direct-current engineeringconvertor station is realized by determining the characteristic parameters of the various lightning arresters, power overvoltage of the convertor station is limited greatly, and design difficulty of engineering and engineering investment level are reduced.