The invention relates to a stair and particularly relates to an assembled stair and an installation method thereof. The invention aims to provide a removable assembled stair, wherein prefabricated parts are transported to the construction site, the prefabricated parts can be assembled and hoisted integrally and can be hoisted independently, and the assembly is carried out in the floor on which the stair needs to be assembled. According to the technical scheme, the assembled stair comprises at least two parallel prefabricated stair beams, prefabricated straining beams and prefabricated pedals, wherein the prefabricated straining beams are arranged at two ends of the prefabricated stair beams so as to play roles in positioning and fixing the prefabricated stair beams, and the prefabricated pedals are arranged on the prefabricated stair beams. According to the removable assembled stair provided by the technical scheme, all parts can be made into finished products on the production site, and then, the parts are transported to the place where the parts need to be installed; the installation is very convenient, and the installation method can be set according to the needs of practical situations; and customers can set the installation method of firstly assembling the parts into the stair and then installing the stair or the installation method of directly assembling the parts on the corridor. The assembled stair is very convenient to use, the cost of the stair is effectively reduced, the construction period is shortened, and the assembled stair can be widely applied to the construction field.