To explore the effects of different organic materials on reducing soil salinity, improving soil fertility and promoting soybean growth in coastal saline soil, five organic materials including corn straw, distiller's grains, flammulina velutipes residue, agaricus bisporus residue and natural humus material (MT) were selected to carry out a pot experiment. Each organic material was set with low, medium and high application rates to study their effects on the physicochemical properties, biological activity, and soybean growth indicators of coastal saline soil. The results showed that different types and application rates of organic amendments played different roles in reducing salinity and improving fertility. High application rate of MT had the best effect on reducing soil salinity, which significantly reduced soil salt content by 1.5 g/kg. Agaricus bisporus residue showed obvious effects on improving soil fertility, which increased the contents of soil organic matter, dissolved organic carbon, and available phosphorus by 71.6%, 278.7% and 89.4%, respectively. Corn straw and flammulina velutipes residue significantly improved soil microbial activities, with high amount of corn straw significantly increased microbial biomass carbon content by 1.5 times, and the high application rate of flammulina velutipes residue significantly increased soil β-glucosidase and N-acetylglucosaminidase activities by 3.3 and 2.6 times. In terms of crop growth promotion and stress resistance, low application rate of flammulina velutipes and agaricus bisporus residue significantly increased the dry weight of soybean biomass by 20.9% and 16.2%, respectively, and decreased the ratio of Na⁺/K⁺by 64.5% and 59.3%, respectively, which benefit to alleviate salt stress on soybean growth. Notably, the high application rate of distiller's grains and agaricus bisporus residue effectively increased soil salt content, intensified salt stress on crops, elevated the content of proline in plant leaves, thereby inhibited crop growth and reduced biomass. Therefore, when using organic materials to improve saline soil, it is imperative to consider the background salinity content of organic amendments and prudently regulate their application amounts to mitigate soil salt accumulation.