To improve the water tree resistance of PE, linear low-density polyethylene (LLDPE) was compounded with sodium acrylate (NaAA) for in situ polymerization, in which NaAA was formed through the neutralization of acrylic acid (AA) with sodium hydroxide (NaOH) before adding dicumyl peroxide (DCP) to initiate the in situ graft polymerization and homo polymerization. A series of LLDPE/NaAA compounds were investigated for their water absorption ratio (WAR)measurement, water treeing, mechanical and dielectric properties. The results strongly suggest that NaAA can improve the water tree resistance of LLDPE. In addition, the LLDPE/NaAA compounds possess satisfactory mechanical properties and dielectric properties. Characterization of LLDPE/NaAA compounds by using Fourier transform infrared spectrometry (FTIR)suggests that the neutralization and polymerization reaction could be achieved effectively. Using adequate DCP content is the key factor for controlling the polymerization of NaAA with precise conversion ratio.