The invention provides a milling and replacement system of electrode caps of spot welding head with fixed resistance of an industrial robot. The system comprises a main framework, a power assembly, a floating damping device, an electrode cap milling mold repairing work and disassembly energy module, an electrode cap storage and installation device and a control module, wherein the main framework comprises a positioning flange, a positioning plate, a supporting shell and a supporting section; the power assembly comprises a motor, a connecting shaft and a driving gear; a driven gear set is arranged in the protective supporting shell and comprises a milling driven system and a disassembly driven system which are engaged with the driven gear; the control module comprises a controller and multiple sensors. Through the structure design, cutting mold repairing and replacement operation can be automatically conducted on the electrode caps by means of the system. It is ensured that the industrial robot completes replacement of positive and negative electrode caps of fixed electrode holder with the simplest motion route, the working efficiency is greatly improved, and the workload of programming is relieved.