Polyethylene Terephthalate (PET) and HDPE (High Density Polyethylene) are the most commonly used polymers in daily life. For biomedical field application, it is need to surface modification to have functional surface. However, no reactive groups on the surface of PET or HDPE. Polymer substrates treated by APT (atmospheric plasma pressure plasma) can activate the surface, therefore could be graft polymerization, because of its simple, low cost and without vacuum. In this study, we using He gas APT to treat HDPE and PET film to formed peroxide groups in surface by APT which are favorable to surface graft polymerization of acrylic acid (Acrylic acid) or thermo-sensitive monomer N-isopropylacrylamide (NIPAAm) on the surface. The results show that after the plasma treatment, the wettability of substrate is change to hydrophilic. The water contact angle of slide glass or PET surface decreases from 68°to 39° after plasma treatment. Graft amount of PNIPAAm gel is 16.7 mg/cm2 on HDPE, and 20.8 on PET . While grafted NIPAAm in wet state would change from colorless to white as temperature higher than lower critical solution temperature (LCST) is 33°C. Keywords: APPD, plasma films, Ethanol, surface graft, NIPAAm.