As one kind of railroad tracks, the slab track already widely applied in the high-speed railroad. In order to satisfy the very high-speed-railroad security and the comfortable need, the request of slab track's ultimate subsidence is very strict during construction and operation. Examined in this paper is the roadbed subsidence rule of Wuhan – Guangzhou railway passenger special line in China. The site observation of roadbed subsidence deformation is utilized and has drawn up the settling curve. Goes a step further, based on the numerical calculus method and the forecast assessment, the roadbed subsidence rule of different ground reinforcement processing has been represented. It is shown that the ultimate subsidence satisfied the request of design and the subsidence deformation of CFG pile compound ground was smaller than that of other ground. These conclusions provide uses for reference importantly to guarantee the quality of slab track on railway passenger special line under construction.