The invention provides a device for installing a rail of a bridge inspection vehicle. The device comprises a bearing platform and a driving mechanism, wherein the bearing platform is used for conveying the to-be-installed rail, and the bearing platform can be hung on the installed rail and can move longitudinally along the installed rail; the driving mechanism can drive the bearing platform to move longitudinally along the installed rail; the bearing platform is of a truss structure, and the second end of the bearing platform can extend out of the second end of the corresponding installed rail. The device can be hoisted on the rail so as to achieve work at the bottom of a bridge, so that bridge floor construction and follow-up passing are not affected; in addition, the device is simple instructure and low in manufacturing cost.