A model of ion energy distribution of dual frequencies capacitively coupled plasma (CCP) has been investigated, it is important to analyze these phenomenon and mechanism in order to control the microelectronic processes of integrated circuit and develop the base theories of plasma physics. We focused on the function of the ion energy distributions under high and low frequencies (dual frequencies) drive in capacitive discharges, we derived a theory model of the dual frequencies driven IEDs from analyzing theories. The model can analyze and predict the IEDs under different high and low frequencies driven, which results in accurate multi-peaks IEDs and energy width for the given control parameters, particle-in-cell (PIC) simulations are used to verify this model.