After the great Wenchuan earthquake broke out on May 12, 2008, more than 10 thousands of aftershocks occurred. China Earthquake Administration performed mobile observation of strong ground motion induced by the aftershocks. With the characteristics and spatial distribution of the aftershocks considered, 59 strong ground motion instruments were installed along Longmenshan fault zone, and more than 2000 records have been accumulated. In this paper, the strong motion records for the largest M6.4 aftershock of May 25, 2008 are preliminary processed and the attenuation relation is obtained. This work shows that it is necessary to perform mobile strong ground motion observation immediately after occurrence of destructive earthquakes, and this would offer precious data for further research.