Manganese slag contains a large number of easily migrated heavy metals and ammonia nitrogen and other pollutants, which have a negative impact on the ecological environment. To verify the feasibility of manganese slag as highway subgrade material, manganese slag samples were solidified by mixing fly ash, cement and quicklime, and the solidification effect was compared. The permeability coefficient, cohesion and internal friction angle of manganese slag were measured by permeability test and triaxial test. On this basis, optimization of manganese slag road sections under different slope heights and different slope ratios in a total of 50 schemes was carried out. GeoStudio software is used to perform finite element simulation on the slope stability of manganese slag slopes under dead weight and rainfall. This study provides a reference for highway construction projects using manganese slag.