Based on the frequency-wavenumber algorithm，we can simulate high frequency (10 Hz) regional seismograms (up to a distance of more than 1000 km). The algorithm is used to synthesize the regional waveguides on Lg waves in a medium consisting of a large number of crustal layers. Based on the crustal velocity model from a former Soviet nuclear test site located in eastern Kazakhstan to WMQ station in China, this paper build up a modified model consisting of thin layers with an alternating high and low-velocity, a velocity gradient near the surface， the lower Q
values， and the composite structure of velocity perturbation and different Q
values so as to match the real crustal structure. And then we simulate very well the regional seismograms in WMQ station by underground nuclear explosions of the test site in eastern Kazakhstan. The synthetic results conform to the energy distribution characteristics of Lg waves, and explain the feature of the coda. The numerical results suggest that the shapes and peak amplitudes of Lg waves all depend on the different crustal waveguides.