The invention discloses an improving method of high liquid limit soil in subgrade engineering. A 'twice lime' method is adopted for clay and high liquid limit soil with the plasticity index more than 25, 3 percent of quicklime is blended in to be braised in the first time, and 2 percent of hydrated lime is blended in before roller compaction in the second time; high liquid limit slit with the plasticity index more than 25 and containing coarse grains is treated through a method with 5 percent quicklime blended in; the high liquid limit slit with the plasticity index less than 25 and the fine grain content above 60 percent and containing coarse grains is treated through a method with quicklime and sand blended in, wherein the content of the quicklime is 5 percent, and the sand blended should meet the requirement that the content of coarse grains is reduced from originally above 60 percent to between 55 percent and 60 percent after the sand is blended in; and the high liquid limit slit with the plasticity index less than 25 and the fine grain content between 50 percent and 60 percent and containing coarse grains is treated through a method with quicklime blended in, and the content of the quicklime blended in is 5 percent. The improvement method of high liquid limit soil in subgrade engineering can significantly reduce the water content of the high liquid limit soil and reduce the liquid limit value and the plasticity index, so as to improve the subgrade engineering quality.