Abstract: The purpose of this study is to investigate the effect of unloading rate on the mechanical response of the backfill and the destabilisation damage mechanism under complex loading conditions. Four different unloading rates of 3, 4, 6 and 8 kPa-s-1 were designed. The backfill plus unloading experiments were carried out using a true triaxial experimental system. The influence of the unloading rate on the backfill energy distribution was analysed based on the energy dissipation principle. The backfill crack information under different unloading rates was obtained and quantitatively analysed by CT scanning experiments. The results show that the backfill enters the yielding phase after the start of unloading. The true triaxial unloading strength of the backfill decreases with increasing unloading rate. The unloading rate has a significant effect on the strain response of the backfill. The equivalence points of σ2 and σ3 and the peak point of σ1 are important stress state change points. As the unloading rate increases, the percentage of elastic energy corresponding to the peak stress point of the backfill gradually decreases. And the percentage of dissipative energy increases with the increase of unloading rate. The unloading action changes the crack distribution within the backfill. The unloading cracks intersect both the σ1σ3 plane and the σ1σ2 plane. And the angle between the unloading cracks and the σ2 direction increases with the unloading rate. The direction of crack propagation in the true triaxial experiment is dominated by the σ3 direction. And the damage percentage increases as the unloading rate increases.