Abstract: Objective Due to the influence of backfill slurry water, water inflow in working face and water accumulation in goaf, the water content of gangue cemented backfill will change with the increase of immersion time, thus changing the bearing performance of the backfill. Studying the strength and damage characteristics of gangue cemented backfill during saturated water immersion is crucial for maintaining the stability of backfill and ensuring the safety of coal mine. Methods By conducting uniaxial compression tests and microscopic electron microscopy scanning tests on the gangue cemented backfill during the saturation immersion process, the variation law of backfill strength with immersion time was analyzed. Based on the statistical distribution of microelement strength, a piecewise damage constitutive model was established in the pre-peak stage. Through microscopic electron microscopy scans, the weakening mechanism of the gangue cemented backfill strength during the saturation immersion process was revealed. Results and Conclusions The results indicate that during the saturated immersion process, the stress-strain curve of the cemented backfill under uniaxial compression exhibits a clear "four stage" characteristic. The maximum strain and stress during the pore crack compaction closure stage, the peak stress point strain and immersion time are positively correlated, while the peak stress and elastic modulus are negatively correlated with immersion time. With the increase of immersion time, the failure mode of the gangue cemented backfill transitions from shear failure to tension shear conjugate failure, and finally transforms into longitudinal tension failure, with the failure location mainly concentrated in the middle of the gangue cemented backfill. The piecewise damage constitutive model considering the maximum stress and strain at the closing stage of pore crack, elastic modulus, peak stress and peak stress point strain was established. The model is verified based on the experimental data, and the curves of the theoretical model are basically consistent with the experimental curves. Under the influence of water tension, lubrication and mineral dissolution, the strength weakening mechanism of gangue cemented backfill in the saturated water tension process is divided into three stages. When the backfill reaches the saturated state, its strength continues to decrease, but the rate of decline decreases. The research results can provide certain data support for gangue cemented backfill mining under water-rich environment in goaf.