With reference to the energy attenuation of electromagnetic wave CT, we present a method for the attenuation inversion of elastic wave CT in an attempt to improve the unsatisfying efficiency of velocity inversion in detecting underground boulders. The square value of the first arrival peak of direct wave was regarded as the waveform energy value. First of all, the coefficient of holistic attenuation in the triangle medium between the single stimulation source and all geophones was calculated after distance correction and normalization processing. Subsequently the coefficient of linear attenuation in the medium from the source to each geophone was calculated according to the fitted relative error. The attenuation coefficient section was then obtained by inversion to be taken as the basis of abnormal discrimination. Practical application of this method to the exploration of boulders in the airport line of Wuhan Metro proves that inversion of attenuation coefficient is more sensitive to small defects than velocity inversion. The relative extreme difference of attenuation coefficient is larger than that of velocity, hence is more conducive to abnormal discrimination.