SiO2/LDPE nanocomposites can effectively decrease space charge accumulation at room temperature. However, space charge build up and suppress mechanism in nanocomposite are still not well understood. Experiments results showed that LDPE has a TSC peak around 60°C and the mechanical loss curve of LDPE which has a peak corresponding to the α-relaxation correspond well to the TSC peak. Space charge of LDPE at different temperatures were obtained by PEA then the sum of space charge amount showed that the space charge curve of LDPE at different temperatures still has a peak and it correspond well to the TSC and DMA peak. These results proved this point of view that space charge accumulation is associated with molecular motions. Compared with LDPE, the DMA loss peak of SiO2/LDPE was lower and shifted to higher temperature which implied that nanoparticles could restrict the movement of LDPE chain. The TSC peak appeared in LDPE is suppressed in SiO2/LDPE nanocomposite and the space charge peak correspond to TSC peak is also suppressed. These experiments results provided some evidences that the space charge suppress mechanisms of LDPE based nanocomposite has correlation with the bound effects on chain movement.