Abstract: To investigate the effect of water migration on methane diffusion in water-bearing coal under transient thermal disturbance, methane desorption-diffusion experiments were conducted on coal samples with different moisture contents. Coal samples were first equilibrated with methane at 4 MPa, followed by negative pressure desorption at 22 ℃ combined with transient heating to 100 ℃. Methane desorption and apparent diffusion coefficients were measured, and molecular dynamics simulations were used to analyze water migration and pore structure evolution. The results show that after transient thermal disturbance, the methane desorption curves of all coal sample groups exhibited a distinct jump, while the magnitude of the response decreased with increasing moisture content; the sample with 6% moisture showed a 26.0% lower response than the 3% sample. Apparent diffusion coefficients decreased after heating, with reductions of 28%-34% for moist samples, higher than for dry coal. Molecular simulations revealed that water molecules respond more strongly to thermal disturbance than methane molecules; they migrate and redistribute, altering the accessible pore space and connectivity, thereby limiting effective diffusion pathways. These findings suggest that transient thermal disturbance can induce short-term methane release, but the pore channel restructuring induced by water migration reduces subsequent diffusion capability, which is an important cause of the attenuation of methane diffusion performance in water-bearing coal samples.