Solid state cathodoluminescence (SSCL) is a new mechanism of light emission in organic-inorganic system. In the present article, we get SSCL under sinusoidal alternating-current voltage with a structure of ITO/SiO2/MEH-PPV/SiO2/Al. The spectra have two peaks: 410 and 580 nm, which obey molecular theory and band model, respectively. The temporal behaviors of both peaks in SSCL are studied with a new method of estimating lifetime in frequency domain. The intensity of the peak at 410 nm decreases as the frequency of the driving voltage increases, and the intensity of the peak at 580 nm increases as the frequency of the driving voltage increases. The difference in the dependence of light intensity on the frequency of excitation comes from the difference in the lifetime of the two peaks. The lifetime of short wavelength emission is found to be less than 5 ms while that of long wavelength emission is more than 0.05 ms.