Isolated power converters are widely used for its safety and flexible adjustment between input and output voltage range. EMI occurs due to the presence of switching process. The existence of parasitic parameters in transformers causes the work of EMI prediction in isolated DC-DC power converters more complicated. Parasitic parameters in transformer are the crucial propagation paths for CM noise conduction. For improving the accuracy of EMI prediction, this paper developed a wide-band frequency transformer model based on the two-capacitance model, further considering both the effect capacitive and inductive coupling on conductive common mode noise. Furthermore, the influence of permeability versus frequency of Mn-Zn ferrite on CM transmission, is investigated in detail. Two-port measurement is used for the validation of the proposed high frequency model. The experiment results demonstrate that the proposed wind-band frequency transformer model can well predict the CM noise behavior in the frequency range of 100 kHz to 100 MHz.