In this work, a kind of semi-interpenetrating polymer network (s-IPN) with unique molecular structures, poly(ethylene glycol) (PEG) network with movable sliding-grafted poly(2-hydroxyethyl methacrylate) (PHEMA) (s-IPN-PEG/alpha-CD-sg- PHEMA), were first reported. s-IPN-PEG/alpha-CD-sg-PHEMAs were prepared by simultaneous "click chemistry" and atom transfer radical polymerization (ATRP) of a mixture of poly(ethylene glycol)-diazide/bromobutyryloxy alpha-cyclodextrin inclusion complex (N-3-PEG-N-3/(alpha-CD-BIBB)(m)), tetrakis(2-propynyloxymethyl) methane (TMOP), CuBr, pentamethyldiethylenetriamine (PMDETA), HEMA and DMF. Attributable to the controlled characters of ATRP and the quantitative yields of "click chemistry", the prepared s-IPN-PEG/alpha-CD-sg-PHEMAs have the well-defined PEG networks, as well as uniform and tunable sliding-grafted PHEMA chains. The length of sliding-grafted PHEMA of the s-IPN-PEG/alpha-CD-sg-PHEMA can be regulated by changing polymerization times. The molecular structures, and physical and thermal properties of the s-IPN-PEG/alpha-CD-sg-PHEMA were studied by FTIR, H-1 NMR, XPS, TGA, and DSC measurements. The s-IPN-PEG/alpha-CD-sg-PHEMAs exhibit good physical and mechanical properties. Most important, comparing to classical semi-IPN, the diffusion of interpenetrated PHEMA from s-IPN-PEG/alpha-CD-sg-PHEMA was largely prevented for a long time solvent immersion because the PHEMA brushes were fixed on PEG networks. The sliding-grafted PHEMA chains afford functionalities to the bulk and surface of s-IPN-PEG and could potentially be used as carriers of genes and drugs.