Paking array in Lanzhou Earth Observatary obtained ten groups of 3-directions strong ground motion records from the main shock of great Wenchuan earthquake.Based on the records the acceleration time history and characteristics of ground motion in loess site are studied.The result shows that peak ground acceleration（PGA） at different point in a small area of same site,with same seismic source and epicentral distance,had a certain degree of difference which obviously effected by site topography.In all ten strong motion observation points,PGA in EW direction were largest and PGA in the vertical direction were smallest.The difference of Fourier spectra in different points,especially for frequencies less than 1 Hz,is insignificant.