Abstract: In order to investigate dielectric properties of nano ZnO/low density polyethylene (LDPE) composites, silane coupling agent and titanium acid ester coupling agent were used to modify nano ZnO, and nano ZnO/LDPE composites with different nano ZnO mass fractions, different nano ZnO particles sizes, different nano ZnO surface modification methods and different cooling methods were prepared by two step method. Then, the dispersion situations of nano ZnO in the matrix, the parameter changings during isothermal crystallization process and trap densities of the composites were investigated by FTIR, SEM, DSC and thermally stimulated current (TSC). Finally, alternate current breakdown, insulation conductivity, permittivity and space charge experiments were conducted under different experimental temperatures respectively. The results show that both the depth and density of trap in nano ZnO/LDPE composites increase due to the addition of nano ZnO. When the particle size of nano ZnO is 40 nm and the mass fraction is 3%, the crystallization rate of the composite is the fastest, the dispersibility of nano ZnO in the matrix is better, the breakdown field strength reaches the highest value 133.3 kV/mm, the conductivity and the dielectric constant are relatively lower, the space charge in the composite is less when voltage application, and the discharge speed is fast when short circuit, and the dielectric properties are better. Since nano particles increase the thermal conduction rate in material and decrease the rate of composites degrading with the temperature increasing, thus comparing with pure LDPE, with experimental temperature rising, the reducing amplitude of breakdown strength and the increasing amplitude of conductivity of nano ZnO/LDPE composites are both smaller.