Abstract: In order to research space charge behavior in low-density polyethylene（LDPE）/Si O₂ nanocomposites, this paper prepared LDPE/Si O₂ nanocomposites with particle size of 15 nm and 50 nm, mass fraction of 5% and elongation of 10%. Space charge behavior of each sample was tested by pulsed electroacoustic apparatus（PEA） method. The results show that homocharge accumulation changes to hetercharge accumulation near electrodes in LDPE/Si O₂ nanocomposites when nanoparticles were added. The amount of space charge increases under tensile condition. There is a large amount of space charge in nanocomposites with elongation of 10% and nanoparticles’ mass fraction of 5%. At the same time, there are two different polarity packet-like space charges in the center of nanocomposites and the packet-like space charge in nanocomposites with particle size of 50 nm is more obvious than that in nancomposites with particle size of 15 nm. This paper explains packet-like space charge by using solitary wave theory, force stressed on charges in nanocomposites and surface charge accumulation of nanocomposites with different dielectric constant, which provides reference for the motion characteristics and distribution characteristics of space charge in nanocomposites.