In order to ensure the long-term service performance of the roadbeds in coastal saline-alkali areas, a series of unconsolidated undrained triaxial tests are conducted on unsaturated sulfate-coated red clay. The stress-strain curves under various dry densities, confining pressures, and salt content conditions are systematically analyzed. Using the grey correlation analysis method, the influence of these factors on the excess stress at the end of each stage and the average stress increase during those stages is quantified. The results show that both the initial tangent modulus and peak strength increase with increasing dry density and confining pressure, but decrease with increasing salt content. It is worth noting that when the salt content is 1% and the confining pressure is not less than 200 kPa, the peak strength increases significantly as the dry density increases; the maximum increase is 222. 88 kPa. However, under the condition where the confining pressure remains at 200 kPa, and the salt content is constant, the increase in peak strength decreases as the dry density increases, with a maximum decrease of 67. 4%. Based on the results of the grey correlation analysis, the soil's mechanical properties are optimal when the dry density is 1. 35 g/cm³ and the salt content is 1%. Further analysis indicates that confining pressure and dry density are the main factors affecting the stress gradients at the end of each stage and the average stress increase during those stages. Among these, confining pressure plays a dominant role in the first stage, while dry density is more significant in the second and third stages. The salt content has only a weak positive impact in the second stage. The findings presented in this paper can serve as a reference for the design and stability analysis of roadbed projects in coastal saline-alkali areas.