Deep coal seams are classified as ultra-low permeability gas reservoirs, characterized by inherently low permeability and micro-scale pore-throat structures. During production, these reservoirs are highly vulnerable to external fluid intrusion, resulting in water-locking damage. To tackle water-locking damage associated with the low permeability of deep coal seams, this study elucidates the microscopic mechanisms of water-unlocking agents, addressing the prior lack of microscopic quantitative characterization. By integrating Low-Field Nuclear Magnetic Resonance (LF-NMR) with physical simulation experiments, we quantitatively analyze fluid retention patterns across various pore-throat scales. Five water-unlocking agents (nonionic, anionic, cationic, zwitterionic, and fluorocarbon) were selected, and their efficacy was evaluated via surface tension, contact angle, and permeability recovery tests. Results indicate that, at a bound water saturation of 53.30%, the water-locking damage rate reaches 87.04%, indicating severe water-locking. LF-NMR analysis shows that fluid retention within small pore-throats (0.001~2.5 ms) accounts for 86.51% of total retention, serving as the primary contributor to water-locking damage. Upon addition of water-unlocking agents, surface tension decreases while contact angles increase. The fluorocarbon-based agent (Type V) exhibited the best performance, reducing surface tension to 19.60 mN/m, increasing contact angle to 48.85°, and achieving a water-locking prevention contribution rate of 81.20%. Following Type V agent treatment, fluid retention in small pore-throats decreased by 31.51%, and permeability recovery reached 28.49%. Small pore-throats serve as the primary seepage channels. As fluid occupancy in smaller pores decreases, gas-phase seepage channels expand, resulting in increased macroscopic permeability. This study accomplishes microscopic quantitative characterization of water-locking damage via LF-NMR, demonstrating that water-unlocking agents alleviate capillary forces to unblock small pore-throat channels, thereby offering novel strategies for efficient deep coal seam development.