In this study, we investigated the molecular dynamics of polyrotaxane (PR), composed of alpha-cyclodextrins (CDs) and a poly(ethylene glycol) (PEG) axial chain, in solution by means of quasi-elastic neutron scattering (QENS) measurements and full-atomistic molecular dynamics (MD) simulations. From QENS experiments, we estimated the diffusion coefficients of CD and PEG monomers in PR, which are in quantitative agreement with those obtained by MD simulations. By analyzing the simulation results, we succeeded, for the first time, in observing and quantifying the sliding motion of CD along a PEG chain. The diffusion coefficient for the sliding motion is almost 6 times lower than that of the translational diffusion of CD in PR at room temperature. The retardation energy barrier on PEG produced by molecular interactions between CD and PEG. We the diffusion coefficient of the sliding dynamics in PR by combining the Einstein-Stokes jump diffusion model. This work provides a general strategy for the molecular designs Potential barrier of the sliding motion is caused by the propose a simple equation to describe diffusion model and a one-dimensional to control the sliding motion in PR.