The invention provides a positioning tool, a mechanical arm system, a surgical system and a registration method. The positioning tool comprises a tool body, a registration tip and a target. One end ofthe tool body is used for being fixed to the tail end of a mechanical arm, and the other end of the tool body is connected with the registration tip. The registration tip is used for abutting againsta preset position. The target is used for being marked on the tool body, the registration tip or the mechanical arm and used for being communicated with navigation equipment. Namely, the tool adoptedby the invention is an integrated registration tool, registration of the mechanical arm and a surgical object can be achieved without the need for replacement of a registration tool in the process, the surgical process is simplified, and the surgical time is shortened. In addition, the target does not need to be repeatedly assembled and disassembled, the navigation equipment can effectively monitor the spatial position of the positioning tool in real time in the whole surgical process, and therefore, the surgical visualization degree and safety are improved.