As an absolutely necessary components to connect all kinds of electronic equipment, cable is one of the key problems of electromagnetic compatibility design, most problems are produced by the cables such as being sensitive to electromagnetic interference, electromagnetic interference emission, signal crosstalk.This paper is aimed at giving the comparative analysis of whether shielding layer should exist in cables or not for electromagnetic interference problem, this paper is aimed at giving the comparative analysis of whether shielding layer should exist in cables or not for electromagnetic interference problem. By using Q3D software to extract the parasitic parameters of the cable and geting the field distribution, establishing the equivalent circuit model of the cable,then using 6500B impedance analyzer to do the measuring and verifying the parasitic parameters of shielded cable and nonmaskable cables,the reason of the shielded cable grounding has been analyzed. The result proves that the inhibitory effect on radiated interference is obvious,though the parasitic parameters of shielded cable increases.