Abstract: During the production of deep coalbed methane (CBM) after fracturing, the output of coal fines and proppants is prone to occur, leading to a decline in well productivity. Conventional experiments on coal particle migration suffer from significant deviations in sample preparation, stress environments, and fluid conditions compared to actual underground reservoir conditions and production practices, casting doubt on the reliability of experimental results. To address the post-fracturing production characteristics of deep coal seams in the Daniudi area, a true triaxial stress experiment was designed to study particle migration within propped fractures. The experiment utilized split cubic coal samples and employed two mixed fluid ratios, high liquid-gas ratio (1∶1) and low liquid-gas ratio (1∶4), to simulate the differences in fluid-gas ratios during early and mid-to-late flowback stages in the target area. By incrementally increasing the displacement flow rate and combining dynamic permeability measurements with solid-phase output analysis, the study systematically investigated the coupled migration mechanisms of coal fines and proppants under varying flow rates and their impact on fracture permeability. The experimental results revealed: As the flow rate increased, the propped fractures exhibited three distinct migration stages: coal fines migration, proppant end-face migration, and proppant deep migration, with the solid-phase output showing two small stepwise increases followed by a rapid surge. The liquid-gas ratio was a critical factor influencing particle migration. The critical migration velocities for both coal fines and proppants under high liquid-gas ratios were lower than those under low liquid-gas ratios, indicating that particle migration is more likely to occur during the early flowback stage of fracturing fluid. Moderate migration of coal fines could slightly enhance permeability by approximately 10%, but excessive migration would trigger a "bridging" effect, blocking pore throats and causing permeability damage of 30%–55%. Proppant migration disrupted the fracture support structure, leading to fluctuating permeability. The established experimental methodology for particle migration in propped coal fractures, along with the related findings, provides strong support for optimizing the drainage strategies of deep CBM and reducing solid-phase production.