An isolating switch mechanism mounting tool comprises a hold hoop. One side of the hold hoop is provided with an opening. An elongated plate is arranged at the opening. The elongated plate is provided with a bolt hole and a bolt. The hold hoop is connected with one end of a positive/negative thread screw assembly at the sidewall. The other end of the positive/negative thread screw assembly is connected with a connector. A U-shaped hold hoop is inserted into the sidewall of the connector and is fixed through the bolt. The positive/negative screw assembly comprises a connecting sleeve which is internally provided with a thread. A positive thread screw and a negative thread screw are connected with two ends of the connecting sleeve in threaded connection. According to the isolating switch mechanism mounting tool, a channel steel component is machined according to field actual dimension on condition of no switch mechanism case; channel steel component machining, channel steel component mounting and switch mechanism case adjustment are successively performed. The number of construction processes is reduced and furthermore working efficiency is improved. Furthermore labor intensity is reduced.