Using Bogoliubov-de Gennes equations, we obtain the self-consistent equation in a ferromagnetic superconductor. Taking into account the rough interface scatteri ng effects, in the framework of the Blonder-Tinkham-Klapwijk model，we present t he differential conductance of the normal metal-insulator-ferromagnet/supercondu ctor (N/I/FS ) tunnel junctions. It is shown that the exchange energy Eh i n FS can lead to the Zeeman splitting of the conductance peaks;the energy differ ence between the two splitting peaks is equal to 2Eh. The differentia l con ductances in N/I/FS are suppressed by the barrier strength and rough interface s cattering strength.