An experimental scheme for the accumulative deformation of subgrade was proposed to study the accumulative deformation law of the subgrade under CＲTS Ⅲ slab track during the design service life． A full-scale CＲTS Ⅲ slab track-subgrade system was introduced，and a 100 million cyclic loading experiment was carried out on the test platform． Test results show that the number of cyclic loading has small influence on dynamic stress of the subgrade; with the increase of cyclic loading times，subgrade accumulative deformation grows fast in the initial stage，and after that the rate of growth gradually decreases; when the cyclic loading reaches 3. 5 million times，it tends to be stable，and after 100 million loading，the final stability value reaches 3. 38 mm． The accumulative deformation of the surface layer of subgrade，bottom layer of subgrade and foundation respectively accounts for 68. 93% ，16. 86% ，8. 88% ，5. 33% of the total accumulative deformation of the subgrade． Finally，an accumulative deformation prediction model was proposed based on the test result，which can provide reference for the establishment of a practical calculation method for the acumulative deformation of high-speed railway subgrade under long-term repeated train loads．