Based on the strong ground motion accelerations recorded by the topographic array in Xishan park of Zigong city for the mainshock of the Wenchuan earthquake，the amplification effects of SDOF system ( damping ratio ζ = 5%) located at the mountain ridge topography were studied with the bidirectional response spectra ratio method，and the results are as follows: ( 1) The amplification effect of topography on horizontal structure is not obvious when frequency is below 1Hz． In the frequency range from 1Hz to 10Hz，the amplification factor of hilltop is maximal，the maximal amplification factor is 3. 25 and the corresponding frequency is 6. 25Hz． In the frequency range from 10Hz to 20Hz，amplification effect of each station tends to be steady， the amplification factor of Station No. 7 in the vicinity of hilltop is maximal，the maximal amplification factor is 2. 3 and the corresponding frequency is 16. 7Hz． ( 2 ) The maximal amplification factors of structure response tend to increase with the elevation of the hills，and the trend in frequency range from 1Hz to 10Hz is more obvious． ( 3 ) Compared with other siteresponse estimation techniques，this method could reflect the influence of topography on structure， which is a better way to study the seismic damage distribution of structures．