In order to be specialized in the mechanical properties of lime-modified red-bed mudstone under different water content in Qianzhang-Changzhou high-speed rail area, compaction tests were carried out on red-bed mudstone and its lime- modified soil, and the mechanical tests of unconfined compression, CBR, direct shear and others were carried out afterwards considering both of the optimal water content and saturated water content. The test result shows that the optimal water content of the modified red mudstone gradually increases while the maximum dry density gradually decreases with the increase of lime content. Lime can significantly improve the strength and bearing capacity of the red mudstone. However, the improvement effect is related to the water content of the red mudstone itself. In the saturated state, the increase of lime content will improve the CBR value and cohesive force, while the improvement effect of unconfined compressive strength and internal friction angle is not as obvious as the former. On the of condition of optimal moisture content, the unconfined compressive strength, cohesion and CBR value gradually get high when the amount of lime blending increases, but the improvement effect on the internal friction angle is not obvious. In addition, the internal friction angle decreases slightly when the lime content exceeds 6%. So it is recommended to use lime to improve the red mudstone in Qianzhangchang area with an optimal mixing ratio of 6%.