To explore the application of sediment from the lower Yellow River in subgrade engineering, the sediment was improved using lime and fly ash. Through a combination of resilient modulus tests, direct shear tests, and ultimate bearing capacity calculations, the road performance of the modified Yellow River sediment was analyzed. The experimental and computational results indicate that when the fly ash content exceeds 40%, the resilient modulus of the modified sediment meets the requirements of relevant standards, though there is a reduction in shear strength. When the lime content exceeds 4%, there is a significant improvement in the resilient modulus, but the effect on shear strength diminishes. Based on the ultimate bearing capacity calculations, considering both timeliness and economic efficiency, the optimal modification scheme for the sediment from the lower Yellow River is determined to be a mixture of 4% lime, 40% fly ash, and a curing time of 7 days.