Aimed at solving two-stage vibration isolation problems in the power assembly of export diesel motor cars, the two-stage vibration isolation system finite element model is established according to structural parameters. The frequency characteristics are mastered by system modal calculation; modal matching analysis is quantitatively performed on the basis of exciting force frequency characteristics; the harmonic response analysis of the system is carried out based on each exciting force frequency; the resonance between frame and unit is accurately judged by the analysis; and the mode matching analysis of rationality is verified. Forced vibration calculation of the system is carried out by applying all exciting forces under idle speed conditions. Then, vibration intensity and transmissibility of the system are obtained from these calculations. The results show that the vibration isolation performance of a two-stage vibration isolation system can satisfy the needs of practical projects, and the research results can provide a reference for practical engineering.