By using a Scanning Electron Microscope (SEM), the tracks of cathode spots on the surface of nanocrystalline Cu cathode produced after the first discharge with peak current of 10 A was investigated. It is found that the movement of cathode spots is sub-directed rather than random. The reason is explained in comparison with conventional Cu. It is suggested that sub-directed walking of cathode spots on the surface of nanocrystalline Cu is beneficial to the diffusion of cathode spots which is responsible for cathode erosion.