The invention discloses a hoistway for additional mounting of an elevator in an existing building. The elevator hoistway comprises a foundation and prefabricated piece bodies connected sequentially on the foundation in an overlaid mode in the vertical direction. The prefabricated piece bodies adopt steel bar concrete structures, are hollow and opened up and down. Prefabricating is conducted in advance outside a site. The two prefabricated piece bodies can be aligned through an upper butt joint structure and a lower butt joint structure to be mounted rapidly. The hoistway has the characteristics of being simple in structure, safe, reliable and high in mounting efficiency in site.