The invention provides an underground mine TBM assembly construction method. The underground mine TBM assembly construction method comprises the following steps that (1) chamber assembly is constructed, and an existing roadway of an underground mine and a chamber assembly expanding excavation section serve as a TBM assembly chamber; and the chamber assembly expanding excavation section is formed through expanding excavation of one end of the existing roadway. (2) TBM parts transportation is constructed, TBM parts are placed on a platform truck through a monorail hoist, and a winch connected with the platform truck is pulled to a preinstalled position. (3) TBM parts assembly is constructed, the TBM parts are installed through a lifting pulley or the monorail hoist, and the TBM installation is finally completed. According to the underground mine TBM assembly construction method, the existing roadway is used as the assembly chamber, a vertical shaft is not needed to be re-excavated on an assembly site, and the feasibility of construction is improved; and large scale equipment of a gantry crane and the like are not needed to be installed under the shaft by using small scale installation equipment of the monorail hoist, the lifting pulley, the winch and the like, the work amount of the expanding excavation and transformation is small, the assembly construction period is shortened, and meanwhile the engineering cost is saved.