The invention relates to the field of robot welding, in particular to a controlling method of spot welding and repair grinding of a robot welding production line. The robot welding production line comprises a programmable logic controller, a spot welding robot set and a station set. The controlling method is characterized by comprising the following steps that (1), the predetermined piece number of spot welding robots needing to be subjected to repair grinding and gun cleaning is set; (2), the spot welding robot set starts welding, till one spot welding robot of the spot welding robot set needs to be subjected to repair grinding; (3), the robot needing to be subjected to repair grinding starts to be subjected to the repair grinding program; (4), repair grinding instructions are sent to the spot welding robots which do not execute any program currently; (5), after the spot welding robots receive the instructions, according to the current welding piece number and compared with the predetermined piece number, whether repair grinding is needed or not is judged, if needed, repair grinding is conducted, and otherwise, repair grinding is not conducted; and (6), the repair grinding process is finished. Compared with the prior art, the problem of repeated waiting caused by disordered repair grinding and gun cleaning of the production line can be effectively prevented. The utilization rate of equipment can be effectively guaranteed, and the beat is improved.