Rock body will generate signals with different frequencies under the impact of external loads. This paper monitors the stress wave signals before and after the rock body is subjected to transient impact loads through the fiber-optic monitoring system with homemade probes, and conducts time-frequency analysis of the experimental monitoring signals using the robust local mean decomposition (RLMD) method combined with the fast Fourier transform (FFT). After that, LS-DYNA software is used to simulate the impact load applied to the rock body and generate the stress wave, and the frequency of the stress wave is verified against the frequency of the experimentally monitored stress wave. Finally, the relationship between the simulated stress wave frequency change under the change of elastic modulus and density is analyzed. Results show that the signals monitored in the field will appear as multiple signals with great amplitude after spectral decomposition of 1500–2300 Hz after the impact is applied in the field, which is consistent with the simulation result of the time-frequency analysis of the stress wave in the main frequency signal of 2203 Hz, and the opposite trend to the frequency change indicated by the one-dimensional planar stress wave derivation, which will be the next step of the research issue.