The invention discloses an installation method of a booster fan for a building smoke exhaust system, and relates to the technical field of building installation. According to the technical scheme, S1,preparation before installation is conducted, specifically, an installation rod is arranged and rotationally connected with a fixed pulley, the fixed pulley is located on the outer side of a buildingand located over the installation position of the booster fan, a lifting rope of a lifting device is wound around the fixed pulley, and the two sides, in the axial direction of the fixed pulley, of the installation rod are both provided with guide ropes; S2, booster fan lifting is conducted, specifically, the lifting rope of the lifting device is connected to the booster fan needing to be installed, the two sides of the booster fan are in sleeving connection with the guide ropes through climbing hooks correspondingly, the lifting device is started to drive the booster fan to move upwards to acorresponding boosting air feeding opening along the two guide ropes; and S3, booster fan installation is conducted, specifically, the booster fan is dragged into the boosting air feeding opening, and the booster fan is installed and fixed through expansion bolts. By arranging the fixed pulley and the lifting device, the time for carrying the booster fan is saved, so that installation of the booster fan is more efficient.