P(MMA/EA)/PEG-TPE semi-interpenetrating polymer networks(S-IPN) were synthesized by PEG-TPE and copolymer of methyl methylacrylate and ethyl acrylate, P(MMA/EA),to improve the compatibility of semi-interpenetrating polymer networks (S-IPN) of polymethyl methyacrylate (PMMA) and polyethylene glycol thermoplastic elastomer (PEG-TPE). The acrylate was entirely converted to its polymer and the translation ratio of PEG-TPE can get to 89% by Fourier transform infrared spectrometer (FTIR) and nuclear magnetic resonance spectrometry(¹H NMR). The transition peak in the P(MMA/EA)/PEG-TPE S-IPNs shifts inward compared with that of PMMA/PEG-TPE, even a single Tg was observed in the composition of 10/90,30/70 in DMA, the flexible morphology was observed from scanning electron micrograph(SEM), which indicates some compatibility and degree of interpenetrating between two polymers in the phases.