Abstract: For detecting the interior conformation and mechanics capability of cement-tailing backfill, the sampling method of bore drilling was adopted from filling blocking walls or other corresponding parts which could cover all the stope to get backfill cores. The acoustic wave velocity of the samples was tested by use of SY-1 type acoustic testing apparatus, and then the spectra and waveforms were analyzed by way of correlative software. Testing results indicate the difference between acoustic wave velocity and elasticity mechanics index derives from the difference of backfill's strengtb and inner density structure. Although different backfill samples have different acoustic speeds, their acoustic waves have similar waveforms and spectrum components basically. The acoustic wave with a longer delay, main spectrum convergence, sententiousness spectra and a higher swing shows that the backfill has little lacuna such as impurities, holes and cavities and its configuration is integrated.