In this paper, the radiated emission and the conducted susceptibility of vehicle electronic circuit to external radio frequency (RF) disturbances are studied using mixed-mode S-parameters method. The analytic method adopting mixed-mode S-parameters developed in this paper can be used to illustrate noise-converting phenomenon and verify successfully by the bulk current injection (BCI) test procedures. The far-field measurement and the susceptible experiment were proved by BCI test and the mixed-mode S-parameters are obtained from four-port vector network analyzer. From the verified results, the correlation of the BCI test agrees very well with the mixed-mode S-parameters method.