Abstract: Based on the traditional engineering approach of calculating the equivalent frequency spectra by the shock response spectrum transformation and using the steady-state amplification factor, an approximate formula for determining the transient amplification factor is presented in this paper for the impact response spectrum relative to the sinusoidal base excitation. Then the influencing factors of the equivalent frequency spectra of the mechanical environment are analyzed with an example of the typical time-domain shock response on the interface between the spacecraft and the launch vehicle. It is shown both by theoretical and numerical analyses that the transient effects of the dynamic loads during the launch phase are so evident that they cannot be accurately symbolized by the traditional approach, since the equivalent frequency spectra change significantly with the Q value, and the spectrum amplitudes are decreased when the Q value increases. Therefore, it can be concluded that the current engineering approach to calculate the equivalent frequency spectra of the mechanical environment for satellites and launch vehicles remains to be improved by more reasonable solutions in the future.