Loess has poor engineering performance and must be treated before it can be used as a roadbed filler. In order to improve the bearing capacity of the loess subgrade, and better solve the engineering disease problem of the loess subgrade, bentonite and lime are added to the loess roadbed filler, and the unconfined compressive strength test and nuclear magnetic resonance test of different combinations of bentonite-lime-loess are carried out. From the perspective of soil strength and pore structure, each content is studied. Bentonite-lime improves the strength and pore structure of loess roadbed fillers. The test results show that bentonite can effectively fill the pores of loess, lime can make the dispersed particles in the soil form a whole, and increase the unconfined compressive strength of the soil by 4.01 times; the unconfined compressive strength of the improved loess increases with the maintenance. Compared with plain loess, the porosity of modified loess decreases, and the proportion of large pores decreases significantly. Scanning through a microscopic electron microscope found that the soil particles were connected as a whole, and the large pores between the particles were basically filled. Therefore, the improvement effect of bentonite and lime on loess filler is more significant.