Abstract: The post-peak damage of the cemented backfill is related to the energy evolution before the peak, and the acoustic emission b-value can effectively reflect the change process of the acoustic emission energy event. The backfill specimens with ash sand ratios of 1∶4, 1∶6, and 1∶8, and curing ages of 7 d, 14 d, and 28 d were prepared. The uniaxial compression tests and acoustic emission tests were carried out to investigate their stress-strain curves and acoustic emission b-value characteristics before and after the peak. The results showed that the steeper the increase of the pre-peak stress-strain curves, the steeper the decrease of the post-peak curves. The pre-peak strain increased linearly with time, and the acoustic emission b-value first increased and then decreased; the post-peak strain rose abruptly with time while the acoustic emission b-value stayed low. The more sharply the acoustic emission b-value dropped before the peak, the more remarkably the strain burst intensified after the peak. A prediction index based on the relative magnitude and slope of the decline in pre-peak acoustic emission b-value was thus proposed, which rose with the increase in the ash sand ratio and the maintenance age, and was consistent with the post-peak strain. These results confirm the method’s capability for pre-peak prediction of post-peak strain behavior.