Using the data of three strong aftershocks after the 2008 Wenchuan earthquake recorded by Gansu strong motion stations,the free field acceleration attenuation in southern Gansu province are studied.The attenuation of Peak Ground Acceleration（PGA） with the epicentral distance follows the exponential law,and the forms of attenuation are parallel.However,the attenuation index of three strong aftershocks also has some differences.The condition of the strong motion stations has certain influence to ground motion intensity and frequency spectrum.So further research to get the universal attenuation law of strong earthquakes in southern Gansu province is needed.