In order to simulate road excitation in time domain appropriately, an analysis was first made on the road excitation in frequency domain based on power spectral density (PSD) of road excitation in spatial frequency. Then a numerical simulation method of road excitation in time domain was derived using filtered white noise. Based on a road excitation simulation in time domain with the filtered white noise method, the sampling frequency of white noise was proposed to be adjusted to the change of the vehicle speed. By analyzing PSD of the generated road excitation in spatial frequency, the generated road excitation in time domain was verified. A comparative study of the road excitation in time domain, and the spectrum as well as the PSD of the road excitations in spatial frequency generated by changing vehicle speed only and that by changing vehicle speed together with the adjusted sampling frequency of white noise show that the latter method agrees well with the standard road classification. A quarter car suspension dynamic performance was simulated with the road excitations generated by different methods, the system response accuracies were compared and analyzed, and thus the importance of the proposed method was validated.