Abstract: Freeze-thaw (F-T) damage profoundly reshapes the initial micro-defect field in fractured rocks, predisposing them to mechanical degradation and macroscopic instability. This study investigates the micro-cracking evolution and failure precursors of fractured sandstone subjected to dry, water-saturated and varying degrees of F-T cycling. By conducting uniaxial compression and concurrent acoustic emission (AE) monitoring, and integrating Fast Fourier Transform (FFT) and Critical Slowing Down (CSD) theory, we characterize the spectral evolution, failure mode mapping, and dynamic precursor responses. The results demonstrate that: (1) Increased F-T cycling and water saturation reduce peak stress while enhancing ductility, accompanied by a decline in cumulative AE energy. (2) AE dominant frequencies exhibit a bimodal distribution, wherein both saturation and F-T action significantly increase the proportion of low-frequency waveforms- a trend most pronounced under saturation. (3) High- and low- frequency components correlate with shear and tensile failure modes, respectively; pore water pressure intensifies tensile failure in saturated specimens, while frost-heaving-induced tensile damage serves as the primary reason for mechanical degradation in F-T cycles. (4) A strong negative correlation is identified between the proportion of low-frequency waveform during initial loading phase and the early warning time (EWT) ratio. F-T pre-damage weakens the rock system's resilience, causing an accelerated onset of CSD characteristics and significantly advancing the macroscopic instability precursor. These insights provide a theoretical basis for evaluating rock mass stability in cold-region engineering.