The invention relates to an assembling tool for a nozzle of a breaker and a positioning assembly of the assembling tool. The assembling tool comprises a gear frame, wherein the gear frame is used for being arranged on the periphery of the corresponding nozzle in a sleeved mode and is matched with the nozzle through the positioning assembly in a rotation stopping mode when used. The lower end of the gear frame is provided with a left pin channel and a right pin channel which correspond to two radial installation holes in the nozzle respectively. The positioning assembly comprises a left positioning pin and a right positioning pin, the left positioning pin and the right positioning pin are used for being inserted in the two radial installation holes in the nozzle in a positioning mode respectively, the left positioning pin and the right positioning pin are correspondingly installed on a first support and a second support respectively, and an elastic retaining structure which enables the left positioning pin and the right positioning pin to be retained in the corresponding pin channels and the corresponding radial installation holes respectively is arranged between the first support and the second support. The positioning assembly enables the gear frame and the nozzle to be positioned firmly and is used in the assembling tool for the nozzle of the breaker.