The invention discloses a four-mechanical-arm climbing type line inspection robot mechanical structure. The distances between two opposite mechanical arms in a four-mechanical-arm group in the direction perpendicular to the extending direction of cables can be adjusted by a width adjusting mechanism, in this way, the distance adjustment between the two cables can be well adapted, and the cables are prevented from bearing too large tension or tensioning force; meanwhile, two mechanical arms in the four-mechanical-arm group are arranged in a swinging manner; therefore, the tightness support adjustment of the two mechanical arms on the cables can be realized through the swinging of the two mechanical arms; the stress of all line rollers is consistent; meanwhile, each line roller is provided with a width detection mechanism for detecting the widths of the two cables and a supporting detection mechanism for detecting the support force of the cables on the line roller. The controller can conduct feedback adjustment on the spatial positions of the four-mechanical-arm group according to the width detection mechanisms and the supporting detection mechanisms, automatic adjustment and controlover the robot are achieved, and the operation stability is guaranteed.