Abstract: The continuous increase in mining intensity has led to frequent rock instability disasters under high ground stress and strong disturbance. Sandstone, as a widely distributed rock type in underground engineering, accurate prediction of its fracture and instability process is the core of mining engineering safety evaluation. In response to the lag of traditional mechanical strength criteria in identifying dynamic disasters triggered by nonlinear evolution of microscopic damage, sandstone samples from the No. 12 coal seam of Buertai Coal Mine of China Energy Shendong Coal Group were collected and subjected to five sets of triaxial compression experiments under different confining pressures. A statistical damage evolution model was constructed based on Weibull distribution and strain strength theory, with a damage evolution index n utilized to characterize the progressive deterioration of the rock. An energy-weighted spatial correlation length was defined using statistical mechanics, where the linkage structure of acoustic emission (AE) event was established via the single-linkage clustering method and weights were assigned based on AE energy products to analyze quantitatively the evolution characteristics of spatial correlation length at different deformation stages and under constrained stress. A comprehensive early-warning index, I_SFW, was proposed by coupling damage increment, external stress driving and microscopic crack topology evolution. The results showed that the spatial correlation length initially exhibited exponential decay due to the random initiation of micro-cracks. However, a significant stepwise increase and spatial structure jump were observed at the critical damage threshold D_c, marking the transition to the spatial collaborative nucleation stage. With increasing confining pressure, the stress threshold required for a specific damage level shifted rightward, accompanied by a decrease in the peak damage evolution rate, which reflected the inhibition and hysteretic effect of high confining pressure on damage revolution. The I_SFW index underwent a nonlinear jump at critical state, with its warning point aligning closely with the internal structural evolution essence. By establishing a coupled relationship between the macroscopic stress field and the mesoscopic spatial structure, this index effectively filters ambient noise and counteracts the inhibition effect of confining pressure, providing a physically meaningful and high-sensitivity criterion for sandstone instability early-warning in deep and complex geological environments.