In this paper, Lg wave records of 43 strong aftershocks in the northern segment of Wenchuan aftershock area recorded by 25 stations of Shaanxi digital network are used. Based on spectral ratio method, a joint inversion method is used to obtain parameters of Lg wave attenuation and site response. In the range of 0.5~7 Hz, the Lg wave attenuation coefficient corresponding to UD, EW and NS components are γ(f)=0.0045f0.327,γ(f)=0.0034f0.417 and γ(f)=0.0036f0.393, respectively. The results show that all stations have site effects lower than 5 in the low frequency, the stations in the Weihe basin as Lint, Jyat and etc do not show obvious amplification, but the stations in the Qinling Mountain show obvious amplification in the high frequencies. At the same time, the results mentioned above are also compared with the that retrieved from small earthquakes.