Abstract: A large amount of free sand is produced during the decomposition of high muddy hydrate reservoir, which will be migrated under the action of gas-liquid seepage. It is easy to lead to the decrease of permeability of gravel packing sand control media, namely permeability damage. Due to permeability damage, productivity is reduced and the long-term effectiveness of sand control gravel is affected. In order to explore the permeability damage of sand control gravel under different influencing factors, we used mixed orthogonal test to conduct sand retention test with different reservoir water contents, test pressure and gravel specifications. We measured the permeability coefficient of sand control medium before and after the test. We observed the phenomenon of sand blocking test and analyzed the law of seepage and permeability damage. The results show the follows. Due to the migration of fine sand, the sand control gravel layer experiences the process from through to blocking and then to through. The seepage of sand resistance test can be divided into four stages: the initial seepage stage(no blockage) to the stable seepage stage(gradual blockage), then to the gas-liquid seepage stage(suddenly dredging), and finally to the gas seepage stage(slight blockage). When the reservoir water content, test pressure and gravel particle size are large, the migration of fine sand in the reservoir is easier. Sand production is more serious, gravel sand control layer seepage damage is more serious. It is worth noting that the permeability damage ratio decreases when the reservoir water content is greater than 125%. The influence degree of permeability damage by different factors is the gravel size of the highest, the test pressure of the second, and the reservoir water content of the third. The influence of gravel size on medium permeability damage is the main factor. The optimal gravel median ratio D₅₀/d₅₀ is 23.6, which is conducive to sand control and gas production. The research results provide a reference for the study of permeability damage of gravel filling sand control medium.