This paper analyzed the strong ground motion records of the 2008 Wenchuan MS
8.0 earthquake at the station GYZJ, and used Matlab software to carry on the fast Fourier transform on the acceleration records of E--W component in 55—75 s, and then obtained a function expression of the acceleration variation with time. The expression contains 50 groups of sine and cosine waves with different frequencies, which are the main composition of the seismic wave. A correlation coefficient of 0.9 deduced from regression analysis shows well fitting between the calculated values and observed records. In addition, we used the SeismoSignal software to analyze the spectrum of the ground motion acceleration. Our results show that the harmonic component with frequency of 2.8 Hz in the original wave has the maximum amplitude and a dominant range of seismic waves has a frequency band of 0—10 Hz. These results generally agree well with the frequency and amplitude distribution of the functional expression. This paper provides an important theoretical basis for the research of wave characteristics and the analysis on the dynamic effect of slope in Wenchuan earthquake.