Free vibration column test is a common testing method for measuring dynamic shear modulus and damping ratio of soil specimen.Because of the influence of environmental factors

such as noises etc

the free vibration attenuation wave curve of soil specimen obtained from the test sometimes may be unsmooth

which leads to incorrect dynamic shear modulus and damping ratio.Software digital filter is an effective method to solve this problem.By comparing with the main advantages and disadvantages of many filters

the average method filter and the inertia method filter can be adopted to solve this problem more effectively for this problem.Suitable parameters of the two filters are chose to obtain smoothing curves of free-vibration attenuation wave.At last

three groups of experimental data are selected to discuss the effectiveness using the average method filter.The result shows that it can eliminate the abnormal results due to high-frequency interfering wave effectively

and thus the desirable results of dynamic shear modulus and damping ratio can be obtained.This result verified the application value of software filter in free vibration column test.