HDPE preirradiated under nitrogen protection was grafted with NIPA/AAc. The grafted hydrogel is temperature and pH sensitive. FTIR, DSC, SEM were used to study the composition, properties and surface morphology of the hydrogel. Results showing that LCST characteristics was different under different pH environment. Under acid condition, hydrogel volume increased with increasing temperature, indicating the hydrogel being heat expansive and temperature sensitive. Under neutral or alkaline condition, hydrogel volume contracted rapidly near phase transition with increasing temperature, indicating the hydrogel being heat shrinking and temperature sensitive.