The invention provides a detecting tool for a rotating shaft welding device. The detecting tool comprises a positioning base. The positioning base is provided with a horizontal positioning face, and the horizontal positioning face is used for supporting the lower side face of a rotary disc of the qualified rotating shaft welding device. The positioning base is provided with at least two rotary disc positioning pins and a lower positioning pin hole, wherein the rotary disc positioning pins can penetrate connecting penetrating holes in the rotary disc of the qualified rotating shaft welding device, the lower positioning pin hole is used for being matched with a lower connecting pin of the qualified rotating shaft welding device, and the lower connecting pin penetrates the lower positioning pin hole from top to bottom. The positioning base is further provided with at least two positioning references. The detecting tool for the rotating shaft welding device further comprises a positioning plate. The positioning plate is correspondingly provided with positioning parts in positioning fit with the positioning references. The positioning plate is further provided with a detecting hole. The detecting hole is provided with an inner hole used for being matched with the peripheral face of an upper connecting pin. When the positioning parts on the positioning plate are in positioning fit with the positioning references, the upper connecting pin on the qualified rotating shaft welding device can penetrate the detecting hole from bottom to top. By means of the tool, the rotating shaft welding device can be rapidly and conveniently detected.