A machine and a method for grinding a spacer grid of a nuclear fuel assembly. The machine includes a spacer grid holding unit, a first rectangular coordinates robot for grinding an outer surface of the spacer grid, a second rectangular coordinates robot for grinding a corner of the spacer grid, and a control unit. The spacer grid holding unit includes a holding jig onto which the spacer grid is seated and held, and a rotary index table which is coupled to the holding jig to rotate the holding jig. The first and second rectangular coordinates robots are provided at predetermined positions adjacent to the spacer grid holding unit. The control unit controls the spacer grid holding unit, the first and second rectangular coordinates robots and all programs required to conduct the operation for grinding the spacer grid.