［Purposes ］ This study investigated the deterioration mechanisms of concrete ’s mechanical properties and microstructures under coupled sulfate and chromate erosion.The research establishes theoretical foundations for durability design and protection of concrete structures in harsh service environments.［Methods］ In practical engineering environments，coupled erosion solutions were prepared with varying sulfate ion，trivalent chromium，and hexavalent chromium concentrations.Wet -dry cycles were applied to simulate erosion processes.The corrosion resistance coefficient of compressive strength and the chloride ion migration coefficient of concrete were investigated.Microstructural morphology was observed using a scanning electron microscope （SEM）.Corrosion products were analyzed through X -ray diffraction （XRD）.［Results］ Compared to the standard curing condition，the compressive strength of concrete decreases by 4.2%-15.1% and the chloride ion migration coefficient increases by 69.2%-384.6% after 90 dry and wet cycles under coupled sulfate and chromium erosion.The analysis shows that the magnitude of change in compressive strength of concrete and chloride ion migration coefficient due to sulfate erosion is greater，while the magnitude of change in compressive strength of concrete and chloride ion migration coefficient due to chromium erosion is less.During the initial sulfate erosion phase，ettringite and gypsum are formed to fill concrete pores.In the later sulfate erosion phase，Ca（OH）2 is consumed and calcium silicate hydrate gel is degraded while ettringite is decomposed into gypsum.Sulfate and chromate penetration depths and content of corrosion products exhibit significant growth with increasing dry -wet cycles.［Conclusions ］ In the coupled sulfate and chromate erosion environment，it is mainly sulfate that dominates concrete deterioration through the calcite and gypsum expansion reaction，while chromium does not affect the morphology of the reaction products of sulfates，and their impact on performance can be disregarded.Moreover，no significant mutual promotion or inhibition is found when the two coexist.Dry-wet cycles accelerate ion migration and pore structure destruction，thus further weakening the durability of concrete.Therefore，for concrete projects in coupled sulfate and chromate erosion environments，the prevention and control measures of sulfate erosion in dry and wet alternating zones should be implemented to prolong the service life of concrete.