<p>To support the safe and efficient underground blasting mining, this paper analyzed the influence of initial pores on the dynamic mechanical properties and energy dissipation characteristics of cemented tailings backfill (CTB). Three different CTB specimens with cement-tailings ratios (c/t) of 1/4, 1/8, and 1/12 were prepared. Nuclear magnetic resonance (NMR) was used to measure their initial porosity differences, and split Hopkinson pressure bar (SHPB) device were conducted to apply impact loading. The results show that: 1) The dynamic peak compressive strength (DPCS) of CTB shows a linear positive correlation with average strain rate (ASR) and a linear negative correlation with initial porosity, with a significant interaction effect between ASR and initial porosity. 2) The CTB damage evolution under impact loading is divided into four stages, among which the plastic yield and post-peak failure stages have the largest proportion of crushing energy dissipation density (<i>e</i>_d) values and are the main damage stages. 3) The crushing energy dissipation (<i>W</i>_d) and <i>e</i>_d of CTB increase exponentially with incident energy (<i>W</i>_I) and ASR, smaller initial porosity leads to smaller growth amplitudes of <i>W</i>_d and <i>e</i>_d, as well as stronger toughness and dynamic compressive capacity of CTB. 4) The CTB specimens mainly exhibit axial tensile failure and pulverization failure, and their fragmentation morphology shifts from block-dominated to powder-dominated with increasing ASR.</p>