Biochar, SMB, was prepared from waste sheep manure and aged under simulated freeze-thaw cyclic conditions, and the effects of freeze-thaw cyclic aging on the performance and behavioral features of SMB when adsorbing methylene blue (MB) dye in water and its influence mechanism were investigated. The results showed that 7~42 cycles of freeze-thaw aging could effectively improve the pore structure of SMB and enhance its adsorption performance. After 14 freeze-thaw cycles, SMB could remove 95.7% of MB under the optimal operating conditions, and the adsorption amount of MB reached 143.5 mg/g, which was 14% higher than that of unaged SMB. When the freeze-thaw cycles reached 49, the pore structure of SMB was damaged, and its adsorption performance deteriorated, and the adsorption amount of MB was 18.8% lower than that before aging. The adsorption behaviors of SMB on MB both before and after freeze-thaw cyclic aging were chemically dominated, multilayered, entropy-driven, spontaneous, and heat-absorbing. Freeze-thaw cyclic aging increased the chemical dominance and spontaneity of adsorption in the shorter term, while decreasing them in the longer term. The adsorption mechanisms all involved electrostatic attraction, pore filling, hydrogen bonding, and π-π bonding interaction, with pore filling being enhanced after shorter-term freeze-thaw cyclic aging. The findings provide broader theoretical support for the application and promotion of SMB in actual pollution management.