In this paper, a Fe-Mn crust sample (CB14) from a seamount in the central Pacific Ocean was studied in detail. Its outer layer can be divided into 5 sub-layers, no hiatus observed between the adjacent sub-layers. The gray-level variation series of the reflectivity of the growth pattern were obtained. The power spectral analysis revealed that most of the prominent cycles identified from gray-level series are corresponding to Milankovitch cycles. Through matching and tuning to the Milankovitch cycles, the authors obtained the growth rates of sub-layer 1 through sub-layer 5 and their corresponding ages. The results show that since Late Miocene, the growth rates of Fe-Mn crust changed alternatively, since recent 1.3 Ma, the growth rate of the Fe-Mn crust slowed down significantly.