Eddy current distribution is important to the performance of planar eddy current probes. In this paper, the Jensen-Shannon divergences of tangential intersection angle spectrum and radial direction energy spectrum were proposed to evaluate the difference between eddy current distributions generated by circular and fractal Koch excitation coils. By the simulation for the circular and Koch shape excitation coils, it works out that the difference of the eddy current distributions between the two kinds of coils becomes larger and larger with an increase in the values of the two Jensen-Shannon divergences. At the same time, the correlation between the change of Jensen-Shannon divergence and the detectability of the short crack in the special direction was discussed through simulation and experiment results. It is found that, relative to the crack in 0° direction, the detectability of the Koch and circular differential pickup probes to the crack in 90° direction has a correlation with the Jensen-Shannon divergence of tangential intersection angle spectrum. The width of each signal generated by the two probes has a correlation with the Jensen-Shannon divergence of radial direction energy spectrum.