Based on 259 horizontal-component digital seismograms recorded on 25 stations of HebeiTelemetered Network

the attenuation model and medium quality factor Q（f）=420. 8f

0.384

of S-wave inCentral and North area of North China are obtained by using a trilinear geometrical spreading model andGA. It is shown that Q（f） in Central and North area of NorthChina is similar to that in Guangdong. Trilinear geometrical spreading model of NorthChina indicates that at a distance less than 50 km

cor-responding to attenuation of the direct wavel amplitudes decay slightly and more rapidly than 1/R. Be-tween 50 and 83 km

where the direct wave is joined by SmS

spectral amplitudes are approximately con-stant. Beyond 83 km

corresponding to the Lg phase

amplitudes decay at a rate that is consistent withR

-0.5

. The result shows that postcritical reflections from the Moho discontinuity play an important role indetermining the shape of the attenuation curve.